Optical fiber pressure sensor

ABSTRACT

The disclosure includes an apparatus including an elongated assembly, at least a portion of which is sized, shaped, or otherwise configured to be inserted into a human body to measure a physiological parameter at an internal location within the body. The elongated assembly includes an elongated member having a first length and an outer surface, a coil disposed about at least a portion of the elongated member, the coil having a second length, and at least one stand-off member positioned between the outer surface of the elongated member and the coil, where the at least one member is configured to prevent the coil from contacting an optical fiber positioned between the elongated member and the coil.

This application is a continuation of U.S. application Ser. No.14/549,287, filed Nov. 20, 2014, which is related to (1) U.S.Provisional Application No. 62/016,379, titled, “OPTICAL FIBER PRESSURESENSOR” to Eberle et al. and filed on Jun. 24, 2014, and to (2) U.S.Provisional Application No. 61/938,558, titled, “OPTICAL FIBER PRESSURESENSOR” to Eberle et al. and filed on Feb. 11, 2014, and to (3) U.S.Provisional Application No. 61/906,956, titled, “OPTICAL FIBER PRESSURESENSOR” to Eberle et al. and filed on Nov. 21, 2013, the entire contentof each being incorporated herein by reference in its entirety, and thebenefit of priority of each is claimed herein.

TECHNICAL FIELD

This document pertains generally to pressure sensing devices, imagingdevices and methods and, in particular, to pressure sensing devices,imaging devices and methods using optical elements and techniques.

BACKGROUND

U.S. Patent Application Publication No. 2009/0180730 to Foster et al. isdirected toward a device for sensing an acoustic signal. The deviceincludes a flexible portion including a laser active region having anemitted wavelength that varies according to a mechanical force acting onthe flexible portion, and including a flexible support member operableto flex or bend according to the acoustic signal. The flexible portionis coupled with the support member so as to cause the flexible portionto flex or bend in accordance with the support member, thereby changingthe emitted wavelength of the laser active region of the flexibleportion.

U.S. Pat. No. 7,680,363 to Wakahara et al. (“Wakahara”) is directedtoward an optical fiber pressure sensor capable of detecting a moreminute pressure change. A base film is formed with a through holepassing through first and second surfaces. An optical fiber is fixed tothe base film at a region other than the Fiber Bragg Grating (FBG)portion, such that the FBG portion is positioned on the through hole inplan view. The optical fiber pressure sensor is attached to an objectbody such that the second surface of the base film is closely attachedto a surface of the object body directly or indirectly.

Overview

The present applicant has recognized, among other things, that otherapproaches to pressure sensing guidewires exhibit mechanical performancesuitable for diagnostic assessment of coronary obstructions, buttypically are not suitable for delivery of therapeutic devices. Thepresent applicant has recognized that the other pressure sensingtechnology, namely piezoresistive or piezocapacitive silicon pressuresensors, and associated electrical cables, are relatively large comparedto the size of the components of a typical therapy delivering guidewire.The present applicant has recognized that the incorporation of suchother pressure sensing technology into a coronary guidewiresubstantially restricts the design of the mechanical components of theguidewire and results in significant compromises to the mechanicalperformance. The present applicant has recognized that a smallerpressure sensing technology, when incorporated into a contemporarycoronary guidewire, would be advantageous in restoring the requiredmechanical performance requirements.

Optical fiber technology can be used in pressure sensors for oildiscovery and production, as well as in larger diagnostic catheters forpatients. The present applicant has recognized that telecommunicationindustry standard optical fiber would be too large to incorporate intohigh performance coronary guidewires.

Accordingly, the present applicant has recognized, among other things,that miniaturization of the optical fiber and optical fiber basedpressure sensor presents both a major challenge and a major advantagefor incorporation into a coronary guidewire while minimizing the impacton the mechanical performance of the guidewire.

The present applicant has recognized, among other things, that theintrinsic sensitivity of an optical fiber sized for insertion into abody lumen may not be sufficient to generate an easily detectable signalwithin the range of pressures associated with a patient. The presentapplicant has recognized that miniaturization of the optical fiber canimpart more flexibility into the fiber. This can be used to mechanicallyenhance the sensitivity of the fiber to pressure, such as with anextrinsic arrangement. The present applicant has recognized that usingFiber Bragg Gratings in the miniaturized optical fiber can provide ahighly cost effective and readily manufacturable design. In addition,the present applicant has recognized that one or more other factors—suchas the temperature coefficient of one or more Fiber Bragg Gratings(FBGs)—can be significantly higher than the intrinsic pressuresensitivity of the optical fiber. As such, a small drift in temperaturewithin a patient can appear as a large pressure change artifact, which,in the context of pressure sensing, is unwanted and likely notacceptable due to the need for accurate pressure measurements.Accordingly, the present applicant has recognized, among other things,that it can be advantageous to provide an optical fiber pressure sensorguidewire that can include temperature calibration, compensation, orcorrection for an optical fiber pressure sensor, such as a Fiber BraggGrating (FBG) arrangement for sensing pressure within a body lumen.

This overview is intended to provide an overview of subject matter ofthe present patent application. It is not intended to provide anexclusive or exhaustive explanation of the invention. The detaileddescription is included to provide further information about the presentpatent application.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, which are not necessarily drawn to scale, like numeralsmay describe similar components in different views. Like numerals havingdifferent letter suffixes may represent different instances of similarcomponents. The drawings illustrate generally, by way of example, butnot by way of limitation, various embodiments discussed in the presentdocument.

FIG. 1 is a cross-sectional side view illustrating generally, by way ofexample, but not by way of limitation, an example of an FBG pressuresensor in an optical fiber.

FIG. 2 is a cross-sectional side view illustrating generally, by way ofexample, but not by way of limitation, an example of an FBG gratinginterferometer sensor.

FIG. 3 is a conceptual diagram illustrating various exampleconfigurations FBG of an optical fiber pressure sensor, in accordancewith this disclosure.

FIGS. 4A-4C depict various conceptual response diagrams related to theconceptual diagram of FIG. 3.

FIG. 5 is a block diagram of an example of an ambient temperaturecompensation technique in accordance with this disclosure.

FIG. 6A is a block diagram of an example of a laser tracking system, inaccordance with this disclosure.

FIG. 6B is a block diagram of an example of a temperature compensationtechnique in accordance with this disclosure.

FIGS. 7A-7C depict an example of a pressure sensor that can be used toimplement various techniques of this disclosure.

FIGS. 8A-8C depict another example of a pressure sensor that can be usedto implement various techniques of this disclosure.

FIGS. 9A-9C depict another example of a pressure sensor that can be usedto implement various techniques of this disclosure.

FIGS. 10A-10D depict another example of a pressure sensor that can beused to implement various techniques of this disclosure.

FIG. 11 depicts a conceptual response diagram related to the example ofa pressure sensor shown in FIG. 10D.

FIGS. 12A-12C depict another example of a pressure sensor that can beused to implement various techniques of this disclosure.

FIGS. 13A-13G depict an example of a guidewire in combination with anoptical fiber pressure sensor, in accordance with this disclosure.

FIGS. 14A-14C depict another example of a guidewire in combination withan optical fiber pressure sensor, in accordance with this disclosure.

FIGS. 15A-15C depict another example of a guidewire in combination withan optical fiber pressure sensor, in accordance with this disclosure.

FIG. 16 depicts another example of a pressure sensor that can be used toimplement various techniques of this disclosure.

FIG. 17 depicts another example of a pressure sensor that can be used toimplement various techniques of this disclosure.

FIG. 18 depicts another example of a pressure sensor that can be used toimplement various techniques of this disclosure.

FIG. 19 depicts another example of a pressure sensor that can be used toimplement various techniques of this disclosure.

FIG. 20 depicts another example of a pressure sensor that can be used toimplement various techniques of this disclosure.

FIGS. 21A-21G depict various examples of a guidewire in combination withan optical fiber pressure sensor, in accordance with this disclosure.

FIG. 22 depicts an example of a combination of a guidewire with anoptical fiber pressure sensor and an imaging sensor, in accordance withthis disclosure.

FIGS. 23A-23B depict another example of a guidewire in combination withan optical fiber pressure sensor, in accordance with this disclosure.

FIG. 24 shows an example of a portion of a concentric pressure sensorassembly.

FIG. 25 shows an example of the pressure sensor assembly as it can beprefinished and included or otherwise incorporated into a percutaneousintravascular guidewire assembly.

FIG. 26 shows an example illustrating how components of the pressuresensor assembly can be integrated into or otherwise incorporated into apercutaneous intravascular guidewire assembly.

FIG. 27 shows an example in which components of the pressure sensingassembly can be retrofitted to or otherwise integrated into an existingguidewire assembly.

FIG. 28 shows an example in which the pressure sensor assembly (e.g., asexplained herein) can be located at a distal end of a guidewireassembly.

FIG. 29A shows an example of a proximal region of a guidewire assembly,such as one of the various guidewire assemblies described herein,terminating at a proximal end connector.

FIG. 29B shows another example of a proximal region of a guidewireassembly, such as one of the various guidewire assemblies describedherein, terminating at a proximal end connector.

FIG. 29C shows another example of a ferrule that can be used incombination with the various guidewire assemblies described herein.

FIG. 29D shows another example of a proximal region of a guidewireassembly terminating at a proximal end connector and using the ferruleof FIG. 29C.

FIG. 30 depicts a conceptual response diagram illustrating the effect ofan uncorrected locking level on a locking wavelength.

FIG. 31 depicts the conceptual response diagram of FIG. 30 compensatedfor optical insertion loss in an optical pressure sensor using varioustechniques of this disclosure.

FIG. 32 is a flow diagram illustrating an example of a method forcompensating for optical insertion loss in an optical pressure sensorusing various techniques of this disclosure.

FIG. 33 is a block diagram of an example of a portion of the lasertracking system of FIG. 6A for compensating for optical insertion lossin an optical pressure sensor using various techniques of thisdisclosure, in accordance with this disclosure.

FIG. 34 depicts a conceptual response diagram illustrating undesirableoptical resonances caused by additional reflection in an optical system.

FIG. 35 depicts the conceptual response diagram of FIG. 34 furtherillustrating undesirable locking circuit wavelength hopping.

FIG. 36 depicts the conceptual response diagram of FIG. 35 compensatedfor optical cavity noise using various techniques of this disclosure.

FIG. 37 depicts a flow diagram illustrating an example of a method forcompensating for optical cavity noise in an optical pressure sensorusing various techniques of this disclosure.

FIG. 38 depicts another example of a portion of a pressure sensorassembly.

FIGS. 39-41 depict examples of portions of various pressure sensorassemblies.

FIG. 42 depicts another example of a guidewire in combination with anoptical fiber pressure sensor.

FIG. 43A-43C depict another example of a guidewire in combination withan optical fiber pressure sensor.

FIG. 44A-44C depict another example of a guidewire in combination withan optical fiber pressure sensor.

FIGS. 45A-45B depict an example of a core wire that can be used incombination with an optical fiber pressure sensor.

FIG. 46A depicts an example of a guidewire in combination with anoptical fiber pressure sensor and the core wire of FIG. 45B.

FIG. 46B depicts a cross-sectional view of the configuration shown inFIG. 46A.

FIG. 47 depicts an example of a guidewire in combination with an opticalfiber pressure sensor assembly that can be used to reduce the effects ofmicrobending, using various techniques of this disclosure.

FIG. 48 depicts another example of a guidewire in combination with anoptical fiber pressure sensor assembly that can be used to reduce theeffects of microbending, using various techniques of this disclosure.

FIG. 49 depicts another example of a guidewire in combination with anoptical fiber pressure sensor assembly that can be used to implementvarious techniques of this disclosure.

FIG. 50 depicts another example of a guidewire in combination with anoptical fiber pressure sensor assembly that can be used to implementvarious techniques of this disclosure.

FIG. 51 depicts another example of a guidewire in combination with anoptical fiber pressure sensor assembly that can be used to implementvarious techniques of this disclosure.

FIG. 52 depicts another example of a guidewire in combination with anoptical fiber pressure sensor assembly that can be used to implementvarious techniques of this disclosure.

FIG. 53 depicts an example of an optical connector that can be used toimplement various techniques of this disclosure.

FIG. 54 depicts an example fusion splice between two optical fibers.

FIGS. 55A and 55B show an example of a proximal region of a guidewireassembly, such as one of the various guidewire assemblies describedherein, terminating at a proximal end connector.

FIGS. 56A and 56B show another example of a proximal region of aguidewire assembly, such as one of the various guidewire assembliesdescribed herein, terminating at a proximal end connector.

FIG. 56C shows another example of a proximal region of a guidewireassembly, such as one of the various guidewire assemblies describedherein, terminating at a proximal end connector.

FIG. 56D shows an example of an optical imaging guidewire assembly.

FIGS. 57A and 57B depict an example of a technique for forming a grooveinto the raw material of the core wire as part of the drawing processfor the core wire.

FIGS. 58A-58B depict another example of a proximal region of a guidewireassembly, terminating at a proximal end connector.

FIG. 59 is a block diagram of another example of a laser trackingsystem, in accordance with this disclosure.

FIG. 60 depicts another example of a portion of a pressure sensorassembly.

FIGS. 61A and 61B depict another example of a portion of a pressuresensor assembly.

FIG. 62 is a block diagram of an example pressure sensing system, inaccordance with this disclosure.

FIG. 63A is a cross-sectional view depicting an example of an opticalfiber having a single coating, in accordance with this disclosure.

FIG. 63B is a cross-sectional view depicting an example of an opticalfiber having a dual coating, in accordance with this disclosure.

FIGS. 64A and 64B are conceptual illustrations of fiber profiles.

FIG. 65 is a flow diagram illustrating another example of a method forcompensating for optical insertion loss in an optical pressure sensorusing various techniques of this disclosure.

FIG. 66 is a flow diagram illustrating another example of a method forcompensating for optical insertion loss in an optical pressure sensorusing various techniques of this disclosure.

FIG. 67A is side view of another example of a pressure sensor housing,in accordance with this disclosure.

FIG. 67B is cross-sectional view of the pressure sensor housing of FIG.67A, in accordance with this disclosure.

FIG. 67C is cross-sectional view of the pressure sensor housing of FIG.67A, including a fused fiber bond, in accordance with this disclosure.

FIG. 68 is a flow diagram illustrating an example of a calibrationtechnique, in accordance with this disclosure.

FIG. 69 is a flow diagram illustrating an example of an offsetprediction technique, in accordance with this disclosure.

DETAILED DESCRIPTION

Before or during an invasive medical procedure, it can be desirable fora clinician, e.g., a physician, to take one or more pressuremeasurements from within a body lumen of a patient, e.g., a bloodvessel, such as an artery or vein. For example, before implanting astent at the site of an occlusion in a blood vessel, it can be desirableto determine the physiologic effect of the occlusion on the patientbefore making a decision whether to implant the stent. Furthermore, itcan also be advantageous to measure the physiologic result of the stentimplantation to ensure that the occlusion has been relieved. One way todetermine the effect of the occlusion on the patient is to measure thedrop in blood pressure across the occlusion, such as using a FractionalFlow Reserve (FFR) technique, an Instantaneous Wave-Free Ratio (iFR)technique, a Post-Interventional Peripheral FFR (pFFR) technique andothers. Generally speaking, according to data generated by long termstudies using the FFR technique, if there is more than a 20-25% drop inpressure across the occlusion during maximum blood flow, the patient canbe considered a candidate for coronary stent implantation. Otherwise, itcan be preferable to treat the patient with a pharmaceutical regimenrather than implant a stent. Occlusions that look visibly similar, usingan intravascular or other imaging modality, can be vastly different interms of pressure drop across the occlusion. Therefore, an accuratemeasurement of pressure drop across an occlusion may help to tease outthose occlusions that should be treated using a stent from thoseocclusions that are adequately treated by a pharmaceutical regimen.

Measurement of pressure in a blood vessel has been achieved byincorporating miniaturized pressure sensors into guidewires that aresmall enough to be steered through the lumen of the vessel without alsocausing an obstruction, which would significantly alter the blood flowand create false pressure readings. These guidewires are typically ofthe same size as the guidewires which are used to treat coronarylesions, for example 0.014″ diameter. However, incorporating pressuresensing capability into a small guidewire typically requires significantvolume of the guidewire being used to accommodate the miniaturizedsensing technology. Often, for example, the solid guidewire core wire isreplaced by a more fragile hollow tube. These changes lead tocompromises in the mechanical performance of the guidewire which canmake it less suitable for delivering therapy, such as a stent in acoronary artery, which leads to time consuming and potentially riskyexchanges of the guidewire as well as increased use of x-rays andcontrast media. Therefore, the present applicant has recognized thatthere is a need to further miniaturize the pressure sensing technologysuch that the incorporation into a steerable guidewire has nosignificant effect on the mechanical performance of the guidewire. Ahigh performance steerable guidewire with on-board highly miniaturizedpressure sensing capability could, therefore, be used throughout aprocedure to both measure the pressure and deliver therapy without theneed to exchange guidewires.

The present applicant has recognized that it is desirable to incorporatehighly miniaturized pressure measurement capability into highperformance guidewires. Additionally, the present applicant hasrecognized that miniaturized pressure sensing capability can be combinedwith other highly miniaturized sensing or imaging technologies toachieve a high performance guidewire that can be used to guide and tofully optimize the treatment of a lesion. By way of example, thepressure sensing capability can be combined with highly miniaturizedintravascular ultrasound (IVUS) imaging sensors to achieve a highperformance guidewire for functional pressure measurement as well asreal-time imaging of vessel structures, previously placed stents,obstructions, blood flow and other uses by itself or in combination withother devices. IVUS imaging is used to create an accurate visual recordof the structure of the blood vessel, enabling accurate on-screenmeasurements of structural dimensions, storage of images, blood flowdetection and visualization, as well as tissue characterization andother techniques.

The present applicant has recognized that a high performance guidewireincorporating highly miniaturized pressure sensing capability as wellas, for example, IVUS imaging, could be used for functional pressureassessment of a lesion prior to treatment, imaging and on-screenmeasurement of the vasculature and lesions, accurate lesion sizing foroptimal stent selection, real-time visually guided optimized stentdeployment, and post-procedural functional measurement to confirmoptimal treatment and other highly valuable uses. Highly miniaturizedIVUS sensors can also be used for flow visualization using Dopplertechniques, correlation techniques and other methods, and also tissuecharacterization, blood velocity measurements and other uses. Multiplearrays of IVUS sensors can be incorporated to create different viewingplanes, such as a forward looking direction, and also 3-dimensionalimaging. The present applicant has recognized that optical sensortechnologies using optical fibers and optical sensors could beminiaturized to achieve the highly miniaturized sensing capabilitiesmentioned above and other sensing capabilities. Furthermore, multiplesensors or combinations of sensor types can be achieved and incorporatedinto a single guidewire. In addition, multiple measurements from thevarious combined sensors can be converted to data for presentation tothe user through separate or combined consoles or modules on one or morescreens or communication devices, or all on a single screen orcommunication device either serially or at once. The data may bedisplayed in real time and may also be recorded for subsequent playbackduring the procedure. The data can also be stored in a data system whichcan allow for entry into the patient record as well as furthersubsequent review.

The present applicant has recognized, among other things, the advantagesand desirability of miniaturization of an optical fiber and opticalfiber based pressure sensor or sensors, and other sensors, forincorporation into a coronary guidewire, which, in turn, can optionallybe used for lesion assessment, guiding a balloon catheter or otherdevice for positioning and securing the stent at the desired location,or for guiding other treatment techniques such as atherectomy, balloonangioplasty, thrombus aspiration, treatment of aneurysms and other uses.

The present applicant has recognized that multiple highly miniaturizedpressure sensors, for example, can be incorporated into a highperformance guidewire. The multiple highly miniaturized pressure sensorscan be in optical communication with a single optical fiber or multipleoptical fibers. Furthermore, the present applicant has recognized thatthe highly miniaturized pressure sensors, and other sensors, can beincorporated into guidewires of multiple different designs, and intoother devices such as catheters or other devices for imaging, such asIVUS and optical coherence tomography, aspiration, treatment and thelike.

The present applicant has recognized that the highly miniaturizedsensors can be incorporated into very low profile catheters which cantrack over the present guidewires described herein as well as overconventional guidewires without sensors on-board. The present applicanthas recognized that the miniaturized sensors can be adapted to variousneeds, for example the number of sensors that can fit into a largerdevice can be more than the number of sensors that can be incorporatedinto a 0.014″ guidewire, for example. Increasing the number of sensorscan allow, for example, the optimization of IVUS imaging in largervessels. Furthermore, the size of the sensors can also be adapted foroptimal functionality when incorporated in other devices. For example,the IVUS sensors can be adapted to operate at other ultrasonicwavelengths by variation of their size. In addition to the abovementioned uses in blood vessels, the guidewire or other devicesincorporating the highly miniaturized sensors could be used in otherplaces within the body for example in the brain, the ovaries, the heart,lungs and other suitable places.

An optical fiber pressure sensor based on FBG technology can have anintrinsic pressure sensitivity of about 0.00038 picometers (pm)/mmHg(about 0.02 pm/psi). Such an optical fiber pressure sensor based on FBGtechnology can have an intrinsic temperature sensitivity of about 10pm/degree Celsius (° C.). The temperature sensitivity can increase ifthe optical fiber pressure sensor includes or is integrated or packagedwith one or more materials having a higher coefficient of thermalexpansion. The range of blood pressures in a patient is relatively low,e.g., about 0 millimeters of mercury (mmHg) to about 300 mmHg, and thereis a need for high resolution within that range, e.g., 1-2 mmHg, where51.7 mmHg equals 1 pound per square inch (psi), such as to adequatelycharacterize the blood pressure drop across a blood vessel occlusion.

Based on these numbers, an uncompensated or uncorrected change intemperature of 0.1° C. can result in an equivalent intrinsic pressuredrift of about 2632 mmHg or more than 1000 times the desired bloodpressure measurement resolution. As mentioned above, when using anoptical fiber pressure sensor capable of insertion into a body lumen ofa patient, e.g., an animal such as a human, a small, uncompensated oruncorrected drift in temperature within the patient, e.g., as a resultof an injected imaging contrast medium, can appear as an artifact thatincorrectly indicates a large change in pressure. This can be due inpart to the relatively low intrinsic sensitivity of the optical fiberpressure sensor to pressure and the relatively high intrinsicsensitivity to temperature of the optical fiber associated with theoptical fiber pressure sensor. As such, a small, uncompensated drift intemperature can be unacceptable due to the need for accurate pressuremeasurements.

Using one or more techniques of this disclosure, a Fiber Bragg Grating(FBG) interferometer or other optical fiber pressure sensor guidewirecan be temperature compensated, such as for permitting accurate pressuresensing within a body lumen. In addition, this disclosure describestechniques for increasing the overall sensitivity of an optical fiberpressure sensor guidewire, such as to generate an easily detectableblood pressure indicating output signal providing the desired resolutionand accommodating the range of pressures associated with the patient.

It should be noted that the optical fiber described in this disclosurecan have a diameter of between about 20 microns and about 80 microns(where a micron is a unit of length equal to one millionth of a meter).By way of comparison, a standard telecommunication optical fiber has adiameter of about 125 microns. This marked reduction in size can causenumerous challenges arising from the differences in the opticsproperties and mechanical behavior of such a drastically reduced sizeoptical fiber.

FIG. 1 is a cross-sectional side view illustrating generally, by way ofexample, but not by way of limitation, an example of a strain-detectingor pressure-detecting optical FBG sensor 100 in an optical fiber 105.The FBG sensor 100 can sense pressure received from a nearby area, andcan transduce the received pressure into an optical signal within theoptical fiber 105. The FBG sensor 100 can include Fiber Bragg gratings110A-B in an optical fiber core 115, such as surrounded by an opticalfiber cladding 120. The gratings 110A-B can be separated by a strain orpressure sensing region 125, which, in an example, can be about amillimeter in length. In an example, strain or pressure can be sensed,such as by detecting a variation in length of the optical path betweenthese gratings 110A-B.

A Fiber Bragg Grating can be implemented as a periodic change in theoptical refractive index of a selected axial portion of the opticalfiber core 115. Light of specific wavelengths traveling down such aportion of the core 115 will be reflected. The period (distance orspacing) 130 of the periodic change in the optical index can determinethe particular wavelengths of light that will be reflected. The degreeof optical refractive index change and the axial length 135 of thegrating 110A-B can determine the ratio of light reflected to thattransmitted through the grating 110A-B.

FIG. 2 is a cross-sectional side view illustrating generally, by way ofexample, but not by way of limitation, an operative example of aninterferometric FBG sensor 100. The example of FIG. 2 can include twogratings 110A-B, which can act as mirrors that can both be partiallyreflective such as for a specific range of wavelengths of light passingthrough the fiber core 115. Generally, the reflectivity of each gratingof a particular pair of gratings 110A-B will be substantially similar tothe other grating in that particular pair of gratings 110A-B, but candiffer between gratings of a particular pair of gratings 110A-B forparticular implementations, or between different pairs of gratings110A-B, or both. This interferometric arrangement of FBGs 110A-B can becapable of discerning the “optical distance or optical pathlength”between FBGs 110A-B with extreme sensitivity. The “optical distance orpathlength” can be a function of the effective refractive index of thematerial of fiber core 115 as well as the physical distance 125 betweenFBGs 110A-B. Thus, a change in the refractive index can induce a changein optical path length, even though the physical distance 125 betweenFBGs 110A-B has not substantially changed.

An interferometer, such as can be provided by the FBG sensor 100, can beunderstood as a device that can measure the interference between lightreflected from each of the partially reflective FBGs 110A-B. When theoptical path length between the FBG gratings 110A-B is an exact integermultiple of the wavelength of the optical signal in the optical fibercore 115, then the light that passes through the FBG sensor 100 will bea maximum and the light reflected will be a minimum, such that theoptical signal can be substantially fully transmitted through the FBGsensor 100. This addition or subtraction of grating-reflected light,with light being transmitted through the optical fiber core 115, can beconceptualized as interference. The occurrence of full transmission orminimum reflection can be called a “null” and can occur at a precisewavelength of light for a given optical path length. Measuring thewavelength at which this null occurs can yield an indication of thelength of the optical path between the two partially reflective FBGs110A-B. In such a manner, an interferometer, such as can be provided bythe FBG optical fiber pressure sensor 100, can sense a small change indistance, such as a change in the optical distance 125 between FBGs110A-B resulting from a received change in pressure. In this manner, oneor more FBG sensors can be used to sense one or more pressures within abody lumen of a patient. This arrangement is an example of an FBGFabry-Perot interferometer, which can be more particularly described asan Etalon, because the physical distance 125 between the FBGs 110A-B issubstantially fixed.

The sensitivity of an interferometer, such as can be included in the FBGsensor 100, can depend in part on the steepness of the “skirt” of thenull in the frequency response. The steepness of the skirt can beincreased by increasing the reflectivity of the FBGs 110A-B, which alsoincreases the “finesse” of the interferometer. Finesse can refer to aratio of the spacing of the features of an interferometer to the widthof those features. To provide more sensitivity, the finesse can beincreased. The higher the finesse, the more resonant the cavity, e.g.,two FBGs and the spacing therebetween. The present applicant hasrecognized, among other things, that increasing the finesse or steepnessof the skirt of FBG sensor 100 can increase the sensitivity of the FBGsensor 100 to pressure within a particular wavelength range but candecrease the dynamic range of the FBG sensor 100. As such, keeping thewavelength of the optical sensing signal within the wavelength dynamicrange of the FBG sensor 100 can be advantageous, such as to provideincreased sensitivity to pressure. In an example, a closed-loop systemcan monitor a representative wavelength (e.g., the center wavelength ofthe skirt of the filtering FBG sensor 100). In response to suchinformation, the closed-loop system can adjust the wavelength of anoptical output laser to remain substantially close to the center of theskirt of the filter characteristic of the FBG sensor 100, even as forcesexternal to the optical fiber 105, such as bending and stress, can causeshifting of the center wavelength of the skirt of the filtercharacteristic of the FBG sensor 100.

In an example, such as illustrated in FIG. 2, the interferometric FBGsensor 100 can cause interference between that portion of the opticalbeam that is reflected off the first partially reflective FBG 110A withthat reflected from the second partially reflective FBG 110B. Thewavelength of light where an interferometric null will occur can be verysensitive to the “optical distance” between the two FBGs 110A-B. Theinterferometric FBG sensor 100 of FIG. 2 can provide another verypractical advantage. In the example illustrated in FIG. 2, the twooptical paths along the fiber core 115 are the same, except for thesensing region between FBGs 110A-B. This shared optical path can ensurethat any optical changes in the shared portion of optical fiber 105 willhave substantially no effect upon the interferometric signal; only thechange in the sensing region 125 between FBGs 110A-110B is sensed.Additional information regarding FBG strain sensors can be found in U.S.Patent Application Publication No. 2010/0087732 to Eberle et al., whichis incorporated herein by reference in its entirety, including itsdisclosure of FBGs and their applications.

FIG. 3 is a conceptual diagram illustrating various examples of FBGconfigurations of an FBG optical fiber pressure sensor 300, inaccordance with this disclosure. The FBG optical fiber pressure sensor300 can include an optical fiber 302 that can extend longitudinallythrough a stiff, rigid, or solid mounting 304. As seen in FIG. 3, aportion of the optical fiber 302 extends beyond a distal end 306 of themounting 304. The optical fiber 302 and the mounting 304 can be disposedwithin a housing 308. Using one or more techniques of this disclosure,such as shown and described in detail in this disclosure with respect toFIGS. 13-15, an optical fiber pressure sensor can include an opticalfiber that can be combined with a guidewire, such as for diagnosticassessment of a coronary obstruction, for example.

As described in more detail below, two or more FBGs, e.g., FBGs 1-4, canbe included in the FBG pressure sensor 300, such as for pressuresensing. One or more additional gratings can be included, and suchadditional one or more gratings can be insulated or isolated frominfluence caused by (1) bending (of the fiber) and/or (2) pressure.These insulated or isolated additional gratings can be arranged forproviding one or more of temperature calibration, compensation, orcorrection. In an example, the additional grating(s) can provide anindependent (of pressure and fiber bending) measure of temperature, suchas for feedback to a temperature compensation scheme or method of anoptical fiber pressure sensor 300. The optical fiber pressure sensor 300can optionally include a sealed or other cavity (not depicted in FIG.3), such as below a portion of the optical fiber 302, e.g., below FBG 3,which can amplify changes in pressure, or otherwise provide increasedoptical response to changes in pressure. Some example configurationsthat can include a sealed cavity are described in more detail below.

In FIG. 3, FBG 1 can be a FBG that produces a broad reflection band atthe center of the spectrum of FBG 1, such as shown generally at 400 inthe response diagram depicted in FIG. 4A, in which the x-axis representswavelength and the y-axis represents the intensity of the reflectedlight. FBG 2 and FBG 3, although depicted and referred to as separategratings, can represent a single FBG that can be split into twoidentical, smaller FBGs and separated by a small phase difference (orphase-shifted) of 180 degrees, for example.

For example, the phase shift could be built into a phase mask that isused to write the gratings onto the fiber, e.g., an electron beamgenerated phase mask. Illumination of the phase mask can result in aphase shift. In another example, a first grating can be written onto thefiber via a phase mask. Then, the phase mask can be moved by a distanceequivalent to a 180 degree phase shift, for example, and a secondgrating can be written onto the fiber.

The reflections from FBG 2 interfere with the reflections from FBG 3because of the phase shift between FBG 2 and FBG 3, shown as a phaseshift region 312A in FIG. 3. As a result, a narrow transmission notch402 is created within the reflection band shown generally at 404 in thewavelength response diagram depicted in FIG. 4A.

In an example, pressure changes can be detected by the optical fiberpressure sensor 300, e.g., within a patient's body, such as by detectingor amplifying the phase-shift between two FBGs, e.g., FBG 2 and FBG 3.This technique is in contrast to optical pressure sensing techniquesthat measure the shift in wavelength of the FBG itself. Using varioustechniques of this disclosure, the phase-shift between FBGs can bemodified rather than a wavelength shift of the FBG itself.

As seen in FIG. 3, FBG 3 can extend distally outward beyond the distalend 306 of the mounting 304. A change in pressure can cause the distalportion 310 of the optical fiber 302 to bend slightly against the distalend 306 of the mounting 304, which, in turn, can cause the distal end306 to mechanically act upon the phase-shift region 312A between FBG 2and FBG 3. The mechanical forces acting upon the phase-shift region 312Abetween FBG 2 and FBG 3 can concentrate a stress in the phase-shiftregion 312A of the optical fiber 302. The concentrated stress in thephase-shift region 312A changes the refractive index of the opticalfiber 302 in the stressed region, which, in turn, can alter, or amplify,the phase relationship between FBG 2 and FBG 3. The change inphase-shift between FBG 2 and FBG 3 can be quantified and the change inpressure can be determined from the quantified phase-shift.

For example, as described in more detail below, a wavelength of a narrowband laser (in relation to the wavelength response of FBGs 2 and 3) canbe locked on a point on a slope 406 of the narrow transmission notch 402in FIG. 4A, e.g., at about 50% of the depth of the notch 402. As thepressure changes, the notch 402 shifts and, consequently, the point onthe slope 406 shifts. A tracking circuit can then track the point on theslope 406, and a phase-shift can be determined from its change inposition. The intensity of reflected light will be modified when thenotch 402 moves. In the example in the diagram, if the notch 402 movesdownward in wavelength, then the intensity of the signal reflected willincrease. If the notch 402 moves upward in wavelength, then theintensity of the signal reflected will decrease. If it is chosen thatthe laser wavelength would be on the opposite side of the notch 402,then the effect would be reversed.

As indicated above, one or more external factors such as the temperaturecoefficient of one or more Fiber Bragg Gratings (FBGs) can besignificantly higher than the intrinsic pressure sensitivity of theoptical fiber pressure sensor that can include such FBGs. As such, asmall drift in temperature within a patient can spuriously appear as alarge change in pressure. Such a temperature-induced artifact in thepressure response signal may be unacceptable due to the need foraccurate pressure measurements. The present applicant has recognized,among other things, that it can be advantageous to provide the opticalfiber pressure sensor guidewire of this disclosure with a temperaturecompensated Fiber Bragg Grating (FBG) arrangement, such as foraccurately sensing pressure within a body lumen, for example.

The conceptual diagram of FIG. 3 can be used to describe severaldifferent configurations for a temperature compensated FBG optical fiberpressure sensor 300. Examples of more detailed configurations are shownand described below with respect to FIGS. 7-10 and FIG. 12.

In a first example of a configuration, a FBG optical fiber pressuresensor 300 can include FBGs 1-3 (FBG 4 need not be included). FBGs 2 and3, which can be configured to operate at the same wavelength (e.g., afirst wavelength between about 1000 nanometers (nm) and about 1700 nm),can form a phase-shift structure that can be used to sense pressure,such as described in detail above. To recap, a concentration in stressin the phase-shift region between the two gratings (e.g., FBG 2 and FBG3), as a result of the bending of the optical fiber 302 changes therefractive index of the optical fiber 302 in the phase-shift region. Thechange in the refractive index of the optical fiber 302 in thephase-shift region can alter the phase relationship between FBG 2 andFBG 3, which can be quantified, and the change in pressure can bedetermined from the quantified phase-shift. The phase-shift, however, isnot compensated for temperature, which may not acceptable, as explainedabove.

FBG 1 can be configured to be substantially independent of pressure,such as by locating it within the stiff, rigid, or solid mounting 308.Therefore, FBG 1 can be used to measure ambient temperature, such as toprovide a temperature compensated optical fiber pressure sensor. FBG 1can be configured to operate at a substantially different wavelengththan that of FBGs 2 and 3 (e.g., a second wavelength between 1000nanometers (nm) and 1700 nm). In this manner, FBG 1 has no interactionwith FBGs 2 and 3. As such, FBG 1 can provide a measure of ambienttemperature that is independent of pressure variations. In a mannersimilar to that described above with respect to tracking the change inposition of the notch 402 of FIG. 4A, a wavelength of a narrow bandlaser (in relation to the response of the FBG 1) can be locked on apoint on a slope 408 of the response of FBG 1 in FIG. 4A, e.g., at about50% of the depth of the response. The wavelength of the locked point onthe slope 408 shifts as the temperature changes. A tracking circuit canthen track the locked point on the slope 408 and a change in ambienttemperature can be determined from its change in position.

In order to generate a pressure signal that is ambient temperaturecompensated, the signal generated by FBG 1 can be used as a reference tonull a shift in temperature. A controller circuit can be configured tocontrol subtraction of the temperature reference signal (from FBG 1)from the temperature and pressure signal (from FBGs 2 and 3), such as togenerate a temperature compensated pressure signal. An example of atemperature compensation technique is described in more detail in thisdisclosure, such as with respect to FIG. 5.

In a second example of a configuration, the FBG sensor 300 can includean optical fiber, a stiff, rigid, or solid mounting, a housing, and FBGs1-3 (FBG 4 need not be included). FBGs 1-3 can be positioned very closeto each other and can thus form a very compact structure. FBGs 2 and 3,which can be configured to operate at the same wavelength (e.g., a firstwavelength between 1000 nm and 1700 nm), can form a phase-shiftstructure that can be used to sense pressure. The phase shift betweenFBGs 2 and 3 can result in a signal that changes with pressure andtemperature.

FBG 1 can be configured to operate at a similar, but slightly different,wavelength than that of FBGs 2 and 3 (e.g., a second wavelength near thefirst wavelength of FBGs 2 and 3 and between 1000 nm and 1700 nm). Inthis manner, FBG 1 can form a resonant feature with FBGs 2 and 3 at aslightly different wavelength. FBG 1 can result in a signal that changeswith respect to temperature changes.

A conceptual illustration of the response of FBGs 1-3 is depicted inFIG. 4B, where the x-axis represents wavelength and the y-axisrepresents the intensity of the reflected light. Again, the techniquesof this disclosure need not sense a shift in the wavelength of thegratings, but can instead sense a change in the phase between thegratings. The temperature compensating element, e.g., FBG 1, is inresonance with part of the pressure sensing structure, e.g., FBGs 2 and3. As such, FBG 1 can be linked to the pressure sensing structure ratherthan being an independent element. Such a configuration can provide acompact structure.

Similar to the first example of a configuration, such as to generate apressure signal that is temperature compensated, the signal generated byFBG 1 can be used as a reference, such as to null a shift intemperature. A slope 410 of the notch 412 and a slope 414 of the notch416 can each be tracked and used to determine changes in temperature andpressure, such as based on their respective changes in position. Acontroller circuit can be configured to control the subtraction of thetemperature reference signal (e.g., from FBG 1) from the temperature andpressure signal (e.g., from FBGs 2 and 3) such as to generate atemperature compensated pressure signal.

In a third example of a configuration, the FBG sensor 300 can include anoptical fiber, a stiff, rigid, or solid mounting, a housing, and FBGs1-4. FBGs 2 and 3, which can be configured to operate at the samewavelength, can form a first phase-shift structure that can be used tosense pressure. The phase shift between FBGs 2 and 3 can result in asignal that changes with pressure or temperature, or both.

FBGs 1 and 4, which can be configured to operate at the same wavelength,can form a second phase-shift structure that can be used to sensetemperature. The reflections from FBG 4 interfere with the reflectionsfrom FBG 1 because of the phase shift between FBG 4 and FBG 1, shown asa phase shift region 312B in FIG. 3. The phase shift between FBGs 1 and4 can result in a signal that changes with temperature and that isindependent of pressure.

A conceptual illustration of the response of FBGs 1-4 of the thirdexample of a configuration is depicted in FIG. 4C, where the x-axisrepresents wavelength and the y-axis represents the intensity of thereflected light. As seen in FIG. 4C, the response includes two notches418, 420. The third example of a configuration can provide more accuratemeasurements than the first example of a configuration because thenotches 418, 420 are generally more sensitive to any changes thanresponses without notches, e.g., the response 400 in FIG. 4A.

Similar to the first and second examples of configurations, in order togenerate a pressure signal that is temperature compensated, the signalgenerated by FBGs 1 and 4 can be used as a reference, such as to null ashift in temperature. A slope 422 of the notch 418 and a slope 424 ofthe notch 420 can each be tracked and used to determine changes intemperature and pressure based on their respective changes in position.A controller circuit can be configured to control subtraction of thetemperature reference signal (e.g., from FBG 1) from the temperature andpressure signal (e.g., from FBGs 2 and 3), such as to generate atemperature compensated pressure signal.

Using any one of the three examples of configurations described above,an optical fiber pressure sensor can be provided that can be suitablefor delivery within a body lumen, e.g., for diagnostic assessment ofcoronary obstructions. In addition, any one of the three examples ofconfigurations can compensate for temperature drift and can be fitted toa guidewire, such as for insertion into a body lumen of a patient. Inany of the three examples the wavelength of the FBGs used fortemperature calibration, compensation, or correction can be above orbelow the wavelength of the FBGs used for the pressure sensing.

Again, FIG. 3 is for conceptual purposes only and this disclosure is notlimited to the three example configurations described above with respectto FIG. 3. Other FBG configurations to sense pressure and compensate fortemperature drift are possible, examples of which are described in moredetail below.

In addition, as described in more detail below, various techniques aredisclosed for increasing the intrinsic sensitivity of an optical fiberpressure sensor, such as to generate an accurate output signal withinthe range of pressures associated with a patient. Generally speaking,these techniques can include focusing a response of a pressure sensormembrane into a smaller area, such as to increase the optical responseto the received pressure, e.g., from pressure waves.

FIGS. 4A-4C depict various wavelength response diagrams related to theconceptual diagram and examples of configurations described above withrespect to FIG. 3. In FIGS. 4A-4C, the x-axis represents wavelength andthe y-axis represents the intensity of the reflected light. The responsediagrams were described above in connection with the examples ofconfigurations of FIG. 3.

FIG. 5 is a block diagram of an example of an ambient temperaturecompensation technique that can be used to implement one or moretechniques of this disclosure. Although the example of a configurationof FIG. 5, shown generally at 500, will be particularly described withspecific reference to the third example of a configuration describedabove, it is applicable to each of the example configurations describedin this disclosure.

Initially, the optical fiber pressure sensor 300 of FIG. 3 can becalibrated, such as to ascertain the relative coefficients oftemperature and pressure for the sensor. The magnitudes of thesecoefficients can be stored in a memory device. A controller circuit canbe configured such that, during operation, it can read the coefficientsfrom the memory device and apply the pressure coefficient as a firstcoefficient X1 and the temperature coefficient as a second coefficientX2.

As described above, a first wavelength of a narrow band laser (inrelation to the response of FBGs 1 and 4) can be locked on a point onthe slope 422 of the narrow transmission notch 418 in FIG. 4C, e.g., atabout 50% of the length of the notch 418. A second wavelength of anarrow band laser (in relation to the response of FBGs 2 and 3) can belocked on a point on the slope 424 of the narrow transmission notch 420in FIG. 4C, e.g., at about 50% of the depth of the notch 420.

As the pressure changes, the notch 420 shifts and, consequently, thepoint on the slope 424 shifts. The tracking circuit can be configured tothen track the point on the slope 424. The magnitude of the change inwavelength, shown as λ1 in FIG. 5, can be input into a first multiplier502 and multiplied by the pressure coefficient X1. Similarly, as theambient temperature of the pressure sensor changes, the notch 418 shiftsand, consequently, the point on the slope 422 shifts. A tracking circuitcan then track the point on the slope 422. The magnitude of the changein wavelength, shown as λ2 in FIG. 5, can be input into a secondmultiplier 504 and multiplied by the ambient temperature coefficient X2.Similarly, The outputs of the multipliers 502, 504 can be input into afirst comparator 506, which can subtract any ambient temperature driftfrom the pressure measurement. In this manner, ambient temperaturenulling techniques can be used to provide accurate pressuremeasurements.

Also in accordance with this disclosure, a third wavelength that can beclose in magnitude to λ1 or λ2 but not in resonance with the phase shiftfeature can be used to monitor a total insertion loss of the system,e.g., from any bending, insertion of the optical fiber into a connector,etc. The insertion loss is generally a static number. During operation,the controller circuit can transmit the third wavelength λ3, which canbe input into a second comparator 508 along with the pressuremeasurement output from a first comparator 506, and the secondcomparator 508 can compensate the pressure measurement for any changesin insertion loss to produce a final pressure reading 510 for theoptical fiber pressure sensor.

Pressure sensors constructed using optical fibers can suffer fromsignificant pressure drift, due at least in part to the low intrinsicsensitivity of optical fibers (e.g., optical refractive index,mechanical size, etc.) to pressure. This is especially true for opticalfiber pressure sensors that are designed for low pressure applications,such as sensing the pressure within the human body.

As mentioned above, when using an optical fiber pressure sensor capableof insertion into a body lumen of a patient, e.g., an animal such as ahuman, a small, uncompensated or uncorrected drift in temperature withinthe patient, e.g., as a result of an injected imaging contrast medium,can appear as an artifact that incorrectly indicates a large change inpressure. This can be due in part to the relatively low intrinsicsensitivity of the optical fiber pressure sensor to pressure and therelatively high intrinsic sensitivity to temperature of the opticalfiber associated with the optical fiber pressure sensor. As such, asmall, uncompensated drift in temperature can be unacceptable due to theneed for accurate pressure measurements.

As described in more detail below with respect to FIGS. 6A-6B, one ormore techniques of this disclosure are described that can remove and/orcompensate for the effects of temperature drifts and other deleteriouseffects that might compromise the accuracy of the pressure reading. Forexample, polarization scrambling techniques, ambient temperature nullingtechniques, laser tracking techniques, and laser temperature monitoringtechniques can be used in combination to correct for temperature driftsthat can affect the accuracy of the pressure readings.

FIG. 6A is a block diagram of an example of a laser tracking system,shown generally at 600, in accordance with this disclosure. A controllercircuit 602 can be configured to control a laser 604 to generate andtransmit the light from a narrow band laser into a first port (e.g.,port 1) of a circulator 606. The circulator 606 can route the light outa second port (e.g., port 2) toward the optical fiber pressure sensor.The controller circuit 602 can be configured to set the wavelength ofthe laser on a point on a slope of a notch in the wavelength response ofan FBG, such as described above. Any light reflected back from theoptical fiber pressure sensor can enter the second port (e.g., port 2)of the circulator 606 and can be routed out a third port (e.g., port 3)and received by an optical detector 608.

As indicated above, laser tracking techniques can be used to correct fortemperature drift. In accordance with this disclosure, the laser 604 canbe actively locked at a position on a slope of a transmission notch,e.g., slope 406 of the notch 402 of FIG. 4A. Then, the system 600 canmeasure the change in wavelength and, in response, alter the laser'soperating characteristics, e.g., drive current.

In the system 600 of FIG. 6A, a first comparator 610 can be used toprovide laser tracking. The optical power of the reflected signal, whichis output by the optical detector 608, can be a first input to a firstcomparator 610. A locking set point value 612 can be a second input tothe first comparator 610. The first comparator 610 can compare the twoinputs and then output a value that can be applied as an input to alaser drive current control 614 that can modulate the drive current ofthe laser 604. In this manner, the configuration of FIG. 6A can providea locking loop to maintain a set point on the slope of a notch, forexample.

In one example implementation, during initial setup a user can adjustthe conditions of the laser 604 so that the wavelength of the laser 604is slightly greater than the wavelength of the transmission notch. Theuser can adjust the wavelength of the laser 604 by adjusting the drivecurrent of a thermoelectric cooler (TEC) of the laser 604 (large shiftsin wavelength), which can alter the temperature of a submount of thelaser 604, or adjust the drive current of the laser 604 itself (smallshifts in wavelength).

Once the initial setup of the laser 604 is complete, the user caninitiate the tracking techniques of this disclosure. The trackingtechniques begin to reduce the drive current to the laser 604, which, inturn, decrease the wavelength of the laser. More particularly, as thewavelength of the laser 604 decreases toward the wavelength of thetransmission notch, the comparator 610 compares the signal from theoptical detector 608 and the locking set point value 612. If the signalfrom the optical detector 608 is higher than the locking set point value612, the drive current of the laser 604 can be reduced via feedback fromthe comparator 610 to the laser drive current control 614. In someexamples, reducing the laser drive current by 0.25 milliamps (mA) canshift the wavelength by 1 pm, where the coefficient of the laser 604 isabout 4 pm per 1 mA of drive current.

During operation, the wavelength of the locked point on the slope canshift as the ambient temperature changes. If the wavelength of thetransmission notch increases or decreases, the system 600 increases ordecreases, respectively, the drive current of the laser 604 in order totrack the transmission notch. As indicated above, the laser 604 can, forexample, be locked on a point on a slope of the narrow transmissionnotch at about 50% of the depth of the notch 402. These trackingtechniques can track the position of the locked point on the slope and achange in temperature can be determined from the change in position. Thedetermined change in temperature can be an input into an algorithmexecuted by a pressure reading module 622, which can use the determinedchange in temperature to calculate an accurate pressure reading. Thepressure reading module 622 can be, for example, machine orcomputer-implemented at least in part. For example, the controller 602can execute instructions encoded on a computer-readable medium ormachine-readable medium that implement the techniques and algorithmsascribed to the pressure reading module 622.

One advantage of tracking the shift in wavelength of the FBG sensor bymodulating the drive current of the laser is that it can linearize theresponse of the circuit and can be more forgiving of different powerlevels. That is, regardless of the built in or fixed insertion loss ofthe pressure sensor, which can vary by construction variables orvariations in connecting in-line optical connectors, the amount by whichthe drive current will change for a given wavelength shift will beconstant. Optical fiber pressure sensors that utilize a change in powerto demodulate the signal are sensitive to changes in insertion loss. Byknowing the shift in laser wavelength for a given drive current change,the current reading can be converted to a wavelength and hence to apressure reading.

Optical sensing schemes exist that directly measure the change inwavelength of the sensor response. In one example, the sensor can beilluminated with broadband light and the spectral response can bemeasured with an Optical Spectrum Analyzer (OSA). This is not feasiblefor this application as the update times can be too slow and therequired wavelength precision is beyond this type of instrument.Alternatively, techniques exist that measure the change in intensity ofthe optical power as the laser tracks up and down the slope of the FBGsensor. One disadvantage of this technique, however, is that the powerresponse will be non-linear for large excursions as the laser approachesthe top of the filter (lower slope) and the bottom of the filter (higherslope). Without compensation this technique can yield inaccurateresults.

Continuing with the description of FIG. 6A, the output of the firstcomparator 610 can be applied as a first input to a second comparator616. A zero pressure DC value 618 can be applied as a second input tothe second comparator 616, which can subtract the initial DC value andoutput a zero pressure reading. The outputted zero pressure reading fromthe second comparator 616 can be multiplied at a multiplier 620 by acoefficient of wavelength shift with the drive current that results inan output of an actual wavelength shift. The outputted actual wavelengthshift can then be converted to a pressure reading at 622.

As indicated above, laser temperature monitoring techniques can be usedto correct for temperature drifts that can affect the accuracy of thepressure readings. The lasers used to implement the various techniquesdescribed in this application have a wavelength dependency on thetemperature at which they operate. A typical laser will have awavelength dependency on operating temperature of 100 pm per degreeCelsius (° C.). A well-controlled laser may have temperature stabilityof 0.01° C. giving a wavelength drift of 1 pm. As indicated above,however, a shift of 1 pm is equivalent to a very large pressuredifference and, as such, should be accounted for in the final pressurereading.

Rather than stabilize the laser temperature to the degree required,which can increase the complexity and expense of the system 600, thisdisclosure describes techniques that can accurately monitor thetemperature through a thermistor that is built-in to the submount of thelaser 604 and that can apply this temperature information to acorrection algorithm for the final pressure reading 622. To accuratelymonitor the temperature through the thermistor, the system 600 of FIG.6A can include an electronic circuit 624, e.g., outside the opticalsystem, that is configured to measure the voltage across the thermistorof the submount of the laser 604. The electronic circuit 624 can includean amplifier that can amplify the voltage signal with high enough gainthat to resolve temperature changes on the order of 1/1000^(th) of adegree Celsius. These changes are on the order of hundreds of microvolts(μV). As such, it can be desirable to use high quality circuits composedof instrumentation amplifiers, for example.

In one example implementation, rather than amplifying the voltage acrossthe thermistor, the electronic circuit 624 can subtract an offsetvoltage from the voltage across the thermistor, e.g., the operatingvoltage of the laser, before amplification. Then, the electronic circuit624 can amplify the resulting voltage value, which is close to zero. Inthis manner, the electronic circuit 624 allows small changes in thetemperature of the laser to be determined. The temperature change can beconverted to wavelength and then to the equivalent pressure, which canthen be used to determine the true pressure reading at 622.

The output from the laser, e.g., laser 604, can have a strong degree oflinear polarization at the exit from the laser package. It istechnically possible to preserve this linear polarization by usingpolarization maintaining fiber and components along the entire opticalpath to the FBGs. If the polarization is preserved such that the lightincident upon the FBGs is aligned preferentially with a particularbirefringent axis, then the response of the light to the FBGs would notbe affected by the birefringence. Unfortunately, preserving thepolarization in this manner is both complex and expensive.

In the absence of polarization maintaining measures, the light from thelaser can arrive at the FBGs with any state of polarization depending onthe nature of the optical path through which the light has travelled.Significant bending or twisting of the fiber and the birefringent natureof any components through which the light has travelled can alter thestate of polarization (SOP). Although the SOP that arrives at the FBGsis not controlled, it nevertheless can have a high degree ofpolarization (DOP) as this characteristic is very difficult to fullyrandomize. A high DOP means the exact interaction of the light and thebirefringent axes of the FBGs can change if there are perturbations tothe system, such as bending of the guidewire during a procedure. Forthis reason, the system 600 of FIG. 6A can utilize polarizationscrambling techniques to overcome the effects of birefringence anddetermine a true pressure reading. The polarization scramblingtechniques scramble or average a range of polarization states so thefinal result is not biased to any given combination of birefringent axisof the FBG and incident polarization state.

Optical fiber pressure sensors such as the FBGs of this disclosure aresubject to the effects of birefringence in the optical fiber, due to thephysical imperfections of the fiber. With birefringence, differentpolarizations of light can have slightly different effective opticalrefractive indices. An effective index of the fiber that is differentfor different polarizations can result in a slightly different Braggwavelength. A different Bragg wavelength can result in the appearance ofmovement of the point on the slope of the transmission notch at whichthe laser is locked. In reality, however, the point may not have movedat all.

A typical optical fiber can have birefringence on the order of 2.5×10⁻⁶,which translates to a wavelength shift between the most differentpolarizations of 4 pm. A 4 pm wavelength shift would be equivalent to arelatively massive pressure change and, as such, should be accounted forin the final pressure reading.

The exact wavelength of the FBG can be determined by a combination ofthe refractive index of the medium and the physical spacing of theplanes or fringes that make up the FBG, as in the following equation:

l _(B)=2n _(e) L,

where l_(B)=Bragg wavelength, n_(e)=effective refractive index, andL=spacing of fringes.

The polarization scrambling techniques of this disclosure can beimplemented by sweeping a series of “optical waveplates” through apseudo-random pattern with sufficient frequency that the desired signalwill be averaged satisfactorily. Optical waveplates are devices that canalter the state of polarization. In order to measure a typicalcardiovascular pressure profile with a heart rate of 0 beats per minuteto 200 beats per minute, scrambling techniques can average at a ratethat is sufficient to capture the dynamic profile, e.g., an effectivefrequency of several hundred hertz.

In the system 600 of FIG. 6A, the optical waveplates can be physicallylocated between where the laser beam exits laser 604 and the FBGs of theoptical fiber pressure sensor. In one example, an optical waveplate canbe formed by wrapping a portion of the optical fiber around apiezoelectric material and by stretching the fiber upon application of avoltage to the piezoelectric material. In another example, an opticalwaveguide can be used to form an optical waveplate. The application of avoltage across electrodes built into the optical waveguide can result inthe change of the refractive index.

Using the polarization scrambling techniques of this disclosure, it isnot necessary to know the levels or patterns of birefringence in thesystem because the polarization controlling techniques do not rely uponfeedback. Instead, the polarization scrambling techniques rely on anaveraged polarization that is achieved by sweeping through as manyavailable polarization states to get an average polarization value sothe final result is not biased to any given combination of birefringentaxis of the FBG and incident polarization state. Additional informationregarding how the polarization scrambling techniques are used todetermine a true pressure reading are disclosed in U.S. ProvisionalApplication No. 61/709,700, titled “POLARIZATION SCRAMBLING FORINTRA-BODY FIBER OPTIC SENSOR”, by Howard Rourke, et al. and filed onOct. 4, 2012, the entire content of which being incorporated herein byreference.

FIG. 6B is a block diagram of an example of a temperature compensationtechnique in accordance with this disclosure. As described above, inorder to determine an accurate pressure reading, both the ambienttemperature of the optical fiber pressure sensor and the temperaturedrift of the laser should be accounted for in the final pressure readingat 622 of FIG. 6A. In FIG. 6B, a first laser 630 can be locked onto aphase-shift region, e.g., phase-shift region 312A between FBG 2 and FBG3 of FIG. 3. This phase-shift region, however, is not compensated forthe ambient temperature of the pressure sensor and, as such, reacts toboth pressure and temperature. Using either a measurement of the changein drive current of the laser, e.g., in milliamps, or a measurement ofthe change in wavelength, the controller 602 of FIG. 6A can determinethe shift in wavelength at 632. Further, using the techniques describedabove, the controller 602 can determine the operating temperature of thefirst laser 630 at 634 by measuring the voltage across the submountthermistor via the electronic circuit 624 of FIG. 6A. The controller 602can correct the determined shift in wavelength for the operatingtemperature of the first laser 630 by subtracting the determinedoperating temperature of the first laser 630 from the shift inwavelength determined at 636. Next, the corrected wavelength shift canbe scaled to an equivalent pressure at 638, e.g., converted from avoltage value to a pressure value. The corrected wavelength shift at 636and its scaled value at 638, however, have not been corrected for theambient temperature of the pressure sensor.

In order to correct for the ambient temperature of the pressure sensor,a second laser 640 can be locked onto another phase-shift region, e.g.,phase-shift region 312B between FBG 1 and FBG 4 of FIG. 3. Thisphase-shift region is insensitive to pressure and responds only to theambient temperature of the pressure sensor. Using either a measurementof the change in drive current of the laser, e.g., in milliamps, or achange in wavelength, the controller 602 of FIG. 6A can determine theshift in wavelength at 642. The controller 602 can also determine thetemperature of the second laser 640 at 644 by measuring the voltageacross the submount thermistor via the electronic circuit 624 of FIG.6A. The controller 602 can correct the determined shift in wavelengthfor the operating temperature of the second laser 640 by subtracting thedetermined operating temperature of the second laser 640 from the shiftin wavelength determined at 646. Next, the corrected wavelength shiftcan be scaled to an equivalent pressure at 648, e.g., converted from avoltage value to a pressure value. Finally, at 650, the pressuredetermined at 648 can be subtracted from the pressure determined at 638in order to determine a true pressure reading.

FIGS. 7A-7C depict an example of a pressure sensor that can be used toimplement one or more techniques of this disclosure. The example of thepressure sensor depicted in FIGS. 7A-7C is an example of a standalonepressure sensor that can use one or more phase shift gratings. The typeof grating written into the fiber can be, for example, a “phase shift”grating or a “Fabry Perot” grating. A “standalone” sensor can be capableof sensing pressure independently of the fiber being attached to a guidewire core subassembly. In contrast, an “integrated” pressure sensor caninvolve placing the fiber with the appropriate gratings written in it ona guide wire core and then completing the sensor once the fiber ispositioned on the wire.

FIG. 7A is an example of a perspective view of an example of a opticalfiber pressure sensor 700 that can include an optical fiber 702, whichcan be configured to transmit one or more optical sensing signals, and atemperature compensated Fiber Bragg Grating (FBG) interferometer (showngenerally at 704 in FIG. 7C) that can be included in, or in opticalcommunication with, the optical fiber 702. The FBG interferometer 704can be configured to receive pressure (e.g., from pressure waves), andto modulate, in response to the received pressure, an optical sensingsignal being delivered via the optical fiber 702 to the FBGinterferometer 704. The pressure sensor 700 can include a sensormembrane 706, which can be in physical communication with the FBGinterferometer 704. The sensor membrane 706 can be configured to helptransmit the pressure to the FBG interferometer 704. The pressure sensor700 can further include a sheath 708 that can, for example, help containcomponents of the pressure sensor 700 and/or help ease the pressuresensor through the vascular system. In some examples, the sensormembrane 706, or any of the sensor membranes referenced in thisdisclosure, can be considered a spring in that its material exhibitslinear elasticity.

FIG. 7B is an example of a cross-sectional end view of the pressuresensor 700 of FIG. 7A. As seen in FIG. 7B, the optical fiber 702 canextend through the pressure sensor 700, such as at substantially anaxial center of the pressure sensor 700.

FIG. 7C is an example of a cross-sectional side view of the pressuresensor 700 of FIG. 7A, such as can be taken along section A-A of FIG.7B. FIG. 7C depicts the optical fiber 702 extending through a proximalportion 710 and a distal portion 712 of the pressure sensor 700. Aproximal portion of the phase shift grating of FBG interferometer 704can be captured by a stiff, rigid, or solid supporting member 714, e.g.,via bonding. The supporting member 714 can be a capillary tube, forexample.

In the distal portion 712, the pressure sensor 700 can define a cavity716, e.g., filled with air, such as laterally below the distal portionof the phase shift grating of FBG interferometer 704 and laterally belowthe remaining distal length of the fiber 702 extending distally axiallybeyond the phase shift grating. In the example shown in FIG. 7C, theflexible sensor membrane 706 can be thick enough such that it contactsthe fiber 702 and the fiber 702 can be attached to the flexible sensormembrane 706, e.g., via bonding. The flexible sensor membrane 706 caninclude, for example, a thin polymer film, a heat seal film, or a thinmetal foil. The flexible sensor membrane 706 can be attached to thepressure sensor 700, such as via bonding or solder. In an example, themembrane 706 can be made by casting a silicone layer.

The pressure sensor 700 can be sealed on both the proximal end 718 andthe distal end 720. In addition, the sensor membrane 706 can be sealedcreating the sealed cavity 706.

The example pressure sensor 700 of FIG. 7C depicts three FBGs, namelyFBGs 1-3, along with an optional FBG, namely FBG 4. FBG 1 is independentof pressure and can be used for temperature measurements to provide atemperature compensated optical fiber pressure sensor, as describedabove with respect to FIG. 3 and FIG. 4A.

FBGs 2 and 3 can form a phase-shift FBG structure. The surface area ofthe membrane 706 can concentrate a change in pressure and can focus amechanical response to the change in pressure at the phase-shift regionbetween FBG 2 and FBG 3. This can enhance the sensitivity of thepressure sensor 700. The mechanical forces acting upon the phase-shiftregion between FBG 2 and FBG 3 can concentrate a stress in thephase-shift region. The concentrated stress in the phase-shift regioncan change the refractive index of the optical fiber 702, which, inturn, alters the phase relationship between FBG 2 and FBG 3. The changein phase-shift between FBG 2 and FBG 3 can be detected and quantified,and the change in pressure can be determined from the quantifiedphase-shift.

In an example, the pressure sensor 700 can optionally further includeFBG 4, e.g., located axially more proximal than FBG 1. As describedabove with respect to FIG. 3 and FIG. 4C, FBGs 1 and 4 can form aphase-shifted FBG structure that can be used to detect and quantify achange in temperature in the pressure sensor 700, which can besubstantially independent of any pressure variations, due to thelocation of FBGs 1 and 4 within the stiff, rigid, or solid supportingmember 714. In the configuration shown in FIG. 7C, the supporting member714 can be disposed about FBGs 1, 2, and 4.

FIGS. 8A-8C depict another example of a pressure sensor that can be usedto implement one or more techniques of this disclosure, such as can usea standalone pressure sensor that can use one or more phase shiftgratings.

FIG. 8A is a perspective view of an example of an optical fiber pressuresensor 800 that can include an optical fiber 802, which can beconfigured to transmit one or more optical sensing signals, and atemperature compensated Fiber Bragg Grating (FBG) interferometer (showngenerally at 804 in FIG. 8C) in optical communication with the opticalfiber 802. The FBG interferometer 804 can be configured to receivepressure (e.g., from pressure waves), and to modulate, in response tothe received pressure, the optical sensing signal. The pressure sensor800 can include a sensor membrane 806 that can be in physicalcommunication with the FBG interferometer 804. The sensor membrane 806can be configured to transmit the pressure to the FBG interferometer804. The pressure sensor 800 can further include a sheath 808 that can,for example, help contain components of the pressure sensor 800 and/orhelp ease the pressure sensor through the vascular system.

FIG. 8B is an example of a cross-sectional end view of the pressuresensor 800 of FIG. 8A. As seen in FIG. 8B, the optical fiber 802 canextend through the pressure sensor 800, such as at substantially anaxial center of the pressure sensor 800.

FIG. 8C is an example of a cross-sectional side view of the pressuresensor 800 of FIG. 8A, such as can be taken along section A-A of FIG.8B. The optical fiber 802 can be supported in part by a stiff, rigid, orsolid supporting member 814. The pressure sensor 800 can defines acavity 816, e.g., filled with air.

As seen in FIG. 8C, the sensor membrane 806 can include a taperedportion 818 that can extend inwardly toward an axial center of thepressure sensor 804. The tapered portion 818 can help focus the responseof the membrane 806 against the phase-shift region between FBG 2 and FBG3, thereby further concentrating a stress in the phase-shift region,which can enhance the sensitivity of the pressure sensor 800.

In an example, a portion of the supporting member 814 can define areservoir 820 that can be adjacent to the fiber 802. The reservoir 820can be filled with a gas, e.g., air. In one example, the reservoir canbe filled with a gas, e.g., nitrogen, that can provide greatertemperature stability than air. In one example, the reservoir 820 can bea vacuum that can provide temperature stability. The reservoir 820 canprovide a configuration that can be adjacent a limited cavity 816immediately laterally below the fiber 802 between FBG 2 and FBG 3 suchthat it can be acted upon by the portion 818 yet the reservoir 820 stillincludes a large compressible volume.

In an example, such as shown in FIG. 8C, the flexible sensor membrane806 can include, for example, a thin polymer film, a heat seal film, ora thin metal foil. The flexible sensor membrane 806 can be attached tothe pressure sensor 800, such as via bonding or solder. In an example,the membrane 806 can be made by casting a silicone layer.

The pressure sensor 800 can be sealed on both the proximal end 817 andthe distal end 819. The sensor membrane 806 can be sealed, such as forcreating the sealed cavity 816.

The example of a pressure sensor 800 of FIG. 8C can include three FBGs(e.g., FBGs 1-3) along with an optional FBG (e.g., FBG 4). FBG 1 can beconfigured to be independent of pressure and can be used for temperaturemeasurement, such as to provide a temperature compensated optical fiberpressure sensor, such as described above with respect to FIG. 3 and FIG.4A.

FBGs 2 and 3 can form a phase-shifted FBG structure. The surface area ofthe membrane 806 can be configured to concentrate a change in pressureonto the portion 818, which can focus a mechanical response to thepressure at the phase-shift region between FBG 2 and FBG 3. Themechanical force acting upon the phase-shift region between FBG 2 andFBG 3 can concentrate a stress in the phase-shift region. Theconcentrated stress in the phase-shift region can change the refractiveindex of the optical fiber 802, such as to alter the phase relationshipbetween FBG 2 and FBG 3. The change in phase-shift between FBG 2 and FBG3 can be detected and quantified, and the change in pressure can bedetermined from the quantified phase-shift.

The pressure sensor 800 can optionally further include FBG 4, e.g.,located axially more proximal than FBG 1. As described above withrespect to FIG. 3 and FIG. 4C, FBGs 1 and 4 can form a phase-shifted FBGstructure that can be used to detect and quantify a change intemperature in the pressure sensor 800. In the configuration shown inFIG. 8C, the supporting member 814 is not disposed about FBGs 1, 2, and4, in contrast to the configuration example of FIG. 7C.

FIGS. 9A-9C depict another example of a pressure sensor that can be usedto implement one or more techniques of this disclosure. The example ofthe pressure sensor depicted in FIGS. 9A-9C can provide a standalonepressure sensor that can use one or more phase shift gratings.

FIG. 9A is a perspective view of an optical fiber pressure sensor 900that can include an optical fiber 902, which can be configured totransmit one or more optical sensing signals, and a temperaturecompensated Fiber Bragg Grating (FBG) interferometer (shown generally at904 in FIG. 9C), such as in optical communication with the optical fiber902. The FBG interferometer 904 can be configured to receive pressure(e.g., from pressure waves), and to modulate, in response to thereceived pressure, the optical sensing signal. The pressure sensor 900can include a sensor membrane 906 that can be in physical communicationwith the FBG interferometer 904. The sensor membrane 906 can beconfigured to transmit the pressure to the FBG interferometer 904. Thepressure sensor 900 can further include a sheath 908 that can, forexample, help contain components of the pressure sensor 900 and/or helpease the pressure sensor through the vascular system.

FIG. 9B is an example of a cross-sectional end view of the pressuresensor 900 of FIG. 9A. As seen in FIG. 9B, the optical fiber 902 canextend through the pressure sensor 900 at a position that is offset froman axial center of the pressure sensor 900.

FIG. 9C is an example of a cross-sectional side view of the pressuresensor 900 of FIG. 9A, such as can be taken along section A-A of FIG.9B. FIG. 9C depicts the optical fiber 902 extending through a proximalportion 910 and a distal portion 912 of the pressure sensor 904. Aproximal portion of the FBG interferometer 904 can be captured by asupporting member 914, e.g., via bonding. The supporting member 914 caninclude a capillary tube, for example. In the distal portion 912, thepressure sensor 900 can define a cavity 916, e.g., filled with air.

As seen in the example shown in FIG. 9C, the sensor membrane 906 can bein mechanical communication with a portion 921 that can extend laterallyinwardly into the pressure sensor 904. The portion 921 can focus theresponse of the membrane 906 against the phase-shift region between FBG2 and FBG 3, which can thereby further concentrate a stress in thephase-shift region, which can enhance the sensitivity of the pressuresensor 900.

In the example shown in FIG. 9C, the flexible sensor membrane 906 caninclude, for example, a thin polymer film, a heat seal film, or a thinmetal foil. The flexible sensor membrane 806 can be attached to thepressure sensor 900, such as via bonding or solder. In an example, themembrane 906 can be made by casting a silicone layer.

The pressure sensor 900 can be sealed on both the proximal end 918 andthe distal end 920. In addition, the sensor membrane 906 can be sealedcreating the sealed cavity 916.

The example of a pressure sensor 900 of FIG. 9C can include three FBGs(e.g., FBGs 1-3), along with an optional FBG (e.g., FBG 4). FBG 1 can beconfigured to be independent of pressure, such as explained above, andcan be used for temperature measurement, such as to provide atemperature compensated optical fiber pressure sensor, such as describedabove with respect to FIG. 3 and FIG. 4A.

FBGs 2 and 3 can form a phase-shifted FBG structure. The surface area ofthe membrane 906 can concentrate any change in pressure into the portion921, which can focus a mechanical response to the pressure at thephase-shift region between FBG 2 and FBG 3. The mechanical forces actingupon the phase-shift region between FBG 2 and FBG 3 can concentrate astress in the phase-shift region. The concentrated stress in thephase-shift region can change the refractive index of the optical fiber902, such as to alter the phase relationship between FBG 2 and FBG 3.The change in phase-shift between FBG 2 and FBG 3 can be detected andquantified, and the change in pressure can be determined from thequantified phase-shift. The pressure sensor 900 can include a compliantlayer 919 laterally underneath the optical fiber 902, such as to allowthe portion 921 to act on the optical fiber 902 without damaging theoptical fiber 902.

The pressure sensor 900 can optionally further include FBG 4, e.g.,located more proximal than FBG 1. As described above with respect toFIG. 3 and FIG. 4C, FBGs 1 and 4 can form a phase-shifted FBG structurethat can be used to quantify a change in temperature in the pressuresensor 800. In the configuration shown in FIG. 9C, the supporting member914 can be disposed about FBGs 1 and 4.

FIGS. 10A-10D depict an example of a pressure sensor that can be used toimplement one or more techniques of this disclosure. The example of apressure sensor depicted in FIGS. 10A-10D can provide an examplestandalone pressure sensor that can use one or more “Fabry Perot”grating arrangements.

FIG. 10A is an example of a perspective view of an optical fiberpressure sensor 1000 that can include an optical fiber 1002, which canbe configured to transmit one or more optical sensing signals, and atemperature compensated Fiber Bragg Grating (FBG) interferometer (showngenerally at 1004 in FIG. 10D) that can be in optical communication withthe optical fiber 1002. The FBG interferometer 1004 can be configured toreceive pressure (e.g., from pressure waves), and to modulate, inresponse to the received pressure, the optical sensing signal. Thepressure sensor 1000 can include a sensor membrane 1006 that can be inphysical communication with the FBG interferometer 1004. The sensormembrane 1006 can be configured to transmit the pressure to the FBGinterferometer 1004. The pressure sensor 1000 can further include asheath 1008 that can, for example, help contain components of thepressure sensor 1000 and/or help ease the pressure sensor through thevascular system.

FIG. 10B is an example of a cross-sectional end view of the pressuresensor 1000 of FIG. 10A, depicting an example of a location of theoptical fiber 1002. As seen in the example of FIG. 10B, the opticalfiber 1002 can extend axially through the pressure sensor 1000, such asat a position that is axially offset from an axial center of thepressure sensor 1000. FIG. 10C is an example of a cross-sectional endview of the pressure sensor without the optical fiber 1002.

FIG. 10D is an example of a cross-sectional side view of the pressuresensor 1000 of FIG. 10A, such as can be taken along section A-A of FIG.10C. FIG. 10D depicts an example of the optical fiber 1002 extendingthrough a proximal portion 1010 and a distal portion 1012 of thepressure sensor 1004. A proximal portion of the optical fiber 1002 canbe captured by a first supporting member 1014A and a distal portion 1012of the optical fiber 1002 can be captured by a second supporting member1014B, e.g., via bonding.

The pressure sensor 1000 can include a sensor member 1006. The pressuresensor 1000 can define a cavity 1016, e.g., filled with air, laterallybelow the sensor membrane 1006. The sensor membrane 1006 and the cavity1016 can concentrate a stress in the area between the Fabry-Perotgratings FBG 1 and FBG 2, which can enhance the sensitivity of thepressure sensor 1000.

The flexible sensor membrane 1006 can include, for example, a thinpolymer film, a heat seal film, or a thin metal foil. The flexiblesensor membrane 1006 can be attached to the pressure sensor 1000, suchas via bonding or solder. In an example, the membrane 1006 can be madeby casting a silicone layer.

The pressure sensor 1000 can be sealed on both the proximal end 1018 andthe distal end 1020. The sensor membrane 1006 can be sealed, such as forcreating the sealed cavity 1016.

The example of a pressure sensor 1000 of FIG. 10D can include four FBGs(e.g., FBGs 1-4). FBGs 3 and 4 can form a phase-shifted FBG structure,such as for sensing temperature. The change in phase-shift between FBG 3and FBG 4 can be detected and quantified, and the change in temperaturecan be determined from the quantified phase-shift, such as describedabove.

The pressure sensor 1000 can further include Fabry-Perot gratings FBG 1and FBG 2, which can be used to sense changes in pressure. Similar tothe phase-shift grating structures described above with respect to FIGS.7-9, the Fabry-Perot gratings FBG 1 and FBG 2 can create a phase shiftthat can be tracked in a manner similar to that described above. Thatis, a notch can be created in the wavelength response to the Fabry-Perotgratings FBG 1 and FBG 2, as shown and described in more detail withrespect to FIG. 11. A point on a slope of the notch can be set andtracked, a phase shift can be detected and quantified, and the change inpressure can be determined from the quantified phase-shift, such asdescribed in detail above.

FIG. 11 depicts an example of a conceptual response diagram related tothe example of a pressure sensor shown in FIG. 10D. In particular, FIG.11 depicts a conceptual wavelength response of the Fabry-Perot gratingsFBG 1 and FBG 2 of FIG. 10D. As seen in the example shown in FIG. 11,the wavelength response of the Fabry-Perot gratings FBG 1 and FBG 2 caninclude three notches, 1100, 1102, 1104. This is in contrast to thewavelength responses of the phase-shift structures shown in FIGS. 4A-4C,which can include a single notch for a pair of FBGs. The additionalnotches in FIG. 11 can be a result of the increased distance between theFabry-Perot gratings FBG 1 and FBG 2. As the distance between theFabry-Perot gratings FBG 1 and FBG 2 increases, additional notches canoccur. As the distance between the Fabry-Perot gratings FBG 1 and FBG 2decreases, notches can disappear until the response resembles that ofthe phase-shift structures described above.

In a manner similar to that described above, a wavelength of a narrowband laser (in relation to the response of FBGs 1 and 2) can be lockedon a point on a slope 1106 of a narrow transmission notch, e.g., notch1102, in FIG. 11, e.g., at about 500/a of the length of the notch 1102.As the pressure changes, the notch 1102 and, consequently, the point onthe slope 1106 shifts. A tracking circuit can then track the point onthe slope 1106 and a phase-shift can be determined from its change inposition. The intensity of reflected light will be modified when thenotch 1106 moves. A phase shift can be quantified, and the change inpressure can be determined from the quantified phase-shift, such asdescribed in detail above.

FIGS. 12A-12C depict another example of a pressure sensor that can beused to implement one or more techniques of this disclosure. The exampleof a pressure sensor depicted in FIGS. 12A-12C can provide anotherexample standalone pressure sensor that can use one or more Fabry-Perotgrating arrangements.

FIG. 12A is an example of a perspective view of an optical fiberpressure sensor 1200 that can include an optical fiber 1202 that can beconfigured to transmit one or more optical sensing signals and atemperature compensated Fiber Bragg Grating (FBG) interferometer (showngenerally at 1204 in FIG. 12C) in optical communication with the opticalfiber 1202. The FBG interferometer 1204 can be configured to receivepressure, e.g., from pressure waves, and to modulate, in response to thereceived pressure, the optical sensing signal. The pressure sensor 1200can include a sensor membrane 1206 that can be in physical communicationwith the FBG interferometer 1204. The sensor membrane 1206 can beconfigured to transmit the pressure to the FBG interferometer 1204. Thepressure sensor 1200 can further include a sheath 1208 that can, forexample, help contain components of the pressure sensor 1200 and/or helpease the pressure sensor through the vascular system.

FIG. 12B is an example of a cross-sectional end view of the pressuresensor 1200 of FIG. 12A. As seen in FIG. 12B, the optical fiber 1202 canextend axially through the pressure sensor 1200 such as at substantiallyan axial center of the pressure sensor 1200.

FIG. 12C is an example of a cross-sectional side view of the pressuresensor 1200 of FIG. 12A, such as can be taken along section A-A of FIG.12B. The optical fiber 1202 can be supported in part by supportingmembers 1214A, 1214B. The pressure sensor 1200 can define a cavity 1216,e.g., filled with air.

As seen in the example of FIG. 12C, the sensor membrane 1206 can includea portion 1218 that can extend inwardly toward a center of the pressuresensor 1204 and that can taper, such as to a point. The portion 1218 canfocus the response of the membrane 1206 against the area between FBG 1and FBG 2, such as for thereby further concentrating a stress in thephase-shift region, which can enhance the sensitivity of the pressuresensor 1200.

A portion of the supporting member 1214 can define a reservoir 1220,such as laterally below the area extending axially between FBG 1 and FBG2. The reservoir 1220 can further enhance the sensitivity of thepressure sensor 1200, such as by allowing the area between FBG 1 and FBG2 to deflect into the reservoir 1220.

In the example shown in FIG. 12C, the flexible sensor membrane 1206 caninclude, for example, a thin polymer film, a heat seal film, or a thinmetal foil. The flexible sensor membrane 1206 can be attached to thepressure sensor 1200, such as via bonding or solder. In an example, themembrane 1206 can be made by casting a silicone layer.

The pressure sensor 1200 can be sealed, such as on both the proximal end1222 and the distal end 1224. The sensor membrane 1206 can be sealed,such as for creating the sealed cavity 1216.

The example of a pressure sensor 1200 of FIG. 12C can include two FBGs(e.g., Fabry-Perot gratings FBG 1 and FBG 2), which can be used to sensechanges in pressure, such as described above with respect to FIG. 10D.The pressure sensor 1200 can optionally further include one or moretemperature compensating FBGs. For example, the pressure sensor 1200 caninclude two additional FBGs (e.g., FBGs 3 and 4 of FIG. 10D), which canform a phase-shifted FBG structure, such as for sensing temperature. Thechange in phase-shift between FBG 3 and FBG 4 can be quantified and thechange in temperature can be determined from the quantified phase-shift,such as described above.

FIGS. 13A-13G depict an example of a guidewire in combination with anoptical pressure sensor. FIG. 13A is an example of a perspective viewillustrating a combination 1300 of a guidewire 1302 and an optical fiber1304 attached to an optical fiber pressure sensor. An optical fiberpressure sensor can be attached at a distal end of the guidewire 1302.The optical fiber 1304 can be disposed in a smooth, rounded groove(groove 1306 of FIG. 13C) extending axially along an outer diameter ofthe guidewire 1302 and optionally helically wound about the guidewire1302, such as within a helically axially extending groove. FIG. 13B isan example of a cross-sectional side view of the combination 1300 ofFIG. 13A, illustrating the optional helical pitch of the combination.

FIG. 13C is an example of a cross-sectional end view of the combination1300 of FIG. 13A, such as can be taken along section A-A of FIG. 13B.The guidewire 1302 can include a solid guidewire with a smooth, roundedgroove 1306 etched out, for example, of the guidewire material (oretched out of a coating thereupon), thereby preserving most of theguidewire material, which can help preserve its mechanical properties.In this manner, the guidewire can be substantially solid, which canavoid the kinking issues that can be associated with hollow guidewires.Using a substantially solid guidewire can improve the guidewire's torquecapabilities. In an example, a coating can be applied over the guidewire1302 and over the fiber 1304, such as to help protect the fiber 1304 orto help secure the fiber 1304 to the guidewire 1302.

In some examples, the guidewires shown and described in this disclosurecan have a maximum diameter (or maximum width if the guidewire does nothave a circular cross-section) of less than about 0.018 inches (18 mil).In one specific example, a guidewire can have a maximum diameter (ormaximum width if the guidewire does not have a circular cross-section)of about 0.014 inches (14 mil).

The grooves in the guidewires shown and described in this disclosureaccount for a small fraction of the overall cross-sectional area of theguidewire. In one specific example, the groove accounts for less thanone percent of the cross-sectional area of the guidewire.

The smooth, shallow, rounded groove in the wire can be placed in thewire before the wire is drawn down to size or it can be etched into thefinal diameter wire using various techniques including lasing,electrodischarge machining, dicing, micromilling, and othermicromachining techniques. In some example implementations, the groovecan be sized to fit the optical fiber outer diameter, which mayincorporate an optical fiber coating, and the thin layer of adhesivethat will hold the optical fiber in the groove with no sharp edges orprotrusions, no material extending beyond the wire diameter at thegroove edges, and a groove surface finish suitable for good adhesiveattachment without being so rough that the optical fiber would besubjected to microstresses when in contact with the groove surface (forexample, a 12 to 16 microinch average surface roughness surface). Thegroove 1306 can be electropolished to achieve the desired surfacequality. A thin hot melt adhesive coating may be coated onto the wireand/or the fiber and then heat-activated when the fiber is laid into thewire groove. Alternatively or additionly, the adhesive (such as a UV orheat curable material) may be applied as the fiber is laid into thegroove or the fiber capture material may be coated over the fiber afterit has been laid in the groove. The guidewire coating materials (such asPTFE, other hydrophobic coatings, or hydrophilic coating materials aswell as heat shrink coverings) may be used to capture the fiber in thegroove, or may be applied around the wire and not to the groove.

FIG. 13D is another example of a cross-sectional end view of thecombination 1300 of FIG. 13A. As seen in FIG. 13D, the groove 1306 canbe a smooth U-shaped groove.

FIG. 13E is another example of a cross-sectional end view of thecombination 1300 of FIG. 13A. As seen in FIG. 13E, the groove 1306 canbe a smooth V-shaped groove.

FIG. 13F is another example of a cross-sectional end view of thecombination 1300 of FIG. 13A. An adhesive 1308 can be either applied tothe groove 1306 or to the optical fiber 1304 or to both in order toaffix the optical fiber 1304 to the groove 1306.

FIG. 13G is another example of a cross-sectional end view of thecombination 1300 of FIG. 13A. FIG. 13G shows an alternativeconfiguration for one or more sections of the groove 1306 that can beshaped to accommodate and retain an optical fiber 1304 having a coating1310. The groove 1306 can have an opening that is slightly smaller thanthe outer diameter of the combination of the optical fiber 1304 and thecoating 1310 to be accommodated. The coating 1310 can be elasticallycompliant or deformable and of sufficient thickness that it may bemechanically pressed into the groove 1306 and retained in place by thenarrower opening of the groove 1306. This mechanical retention can beuseful for temporarily or permanently holding the optical fiber 1306 inplace during or after assembly. This arrangement may be used inconjunction with adhesives or coatings to optimize the placement andaccommodation of the optical fiber along its length.

FIGS. 14A-14C depict an example of a guidewire in combination with anoptical fiber pressure sensor. FIG. 14A is an example of a perspectiveview illustrating a combination 1400 of a guidewire 1402 and an opticalfiber 1404 that can be attached to an optical fiber pressure sensor. Anoptical fiber pressure sensor can be attached at a distal end of theguidewire 1402. The optical fiber 1402 can be disposed in a flat groove(flat groove 1406 of FIG. 14C) extending axially along an outer diameterof the guidewire 1402 (or along a coating thereupon) and optionallyhelically wound about the guidewire 1402. FIG. 14B is a cross-sectionalside view of the combination 1400 of FIG. 14A, illustrating the helicalpitch of the combination. The helical design can allow any stresses,e.g., from compression and tension, to be more evenly distributed alongthe length of the guidewire.

FIG. 14C is a cross-sectional end view of the combination 1400 of FIG.14A, such as can be taken along section A-A of FIG. 14B. The guidewire1402 can include a solid guidewire with a flat groove 1406 etched out,for example, of the guidewire material, or a coating thereupon, therebypreserving most of the guidewire material and the mechanical propertiesassociated therewith. In this manner, the guidewire can be substantiallysolid, which can help avoid the kinking issues that can be associatedwith hollow guidewires. Using a substantially solid guidewire canprovide better torque capability of the guidewire. In an example, acoating can be applied over the guidewire 1402 and the fiber 1404, suchas to help protect the fiber 1404 or to help secure the fiber 1404 tothe guidewire 1402.

FIGS. 15A-15C depict an example of a guidewire in combination with anoptical fiber pressure sensor. FIG. 15A is an example of a perspectiveview illustrating a combination 1500 of a multifilar guidewire 1502 andan optical fiber 1504 that can be attached to an optical fiber pressuresensor. An optical fiber pressure sensor can be attached at a distal endof the guidewire 1502. The optical fiber 1504 can be disposed in aninterstice between filaments of the multifilar guidewire 1502 andoptionally axially helically wound about the guidewire 1502. FIG. 15B isan example of a cross-sectional side view of the combination 1500 ofFIG. 15A, illustrating an example of the helix pitch of the combination.

FIG. 15C is an example of a cross-sectional end view of the combination1500 of FIG. 15A, such as can be taken along section A-A of FIG. 15B.The multifilar guidewire 1502 can include multiple filaments 1506. Theoptical fiber 1504 can be disposed in an interstice between twofilaments 1506, for example, toward an outer diameter of the guidewire1502. In this manner, the guidewire can be substantially rigid, like asolid guidewire, which can help avoid the kinking issues that can beassociated with hollow guidewires. Using a substantially solid guidewirecan help provide desired torque capability of the guidewire. In anexample, a coating can be applied over the guidewire 1502 and the fiber1504, such as to help protect the fiber 1504 or to help secure the fiber1504 to the guidewire 1502.

FIG. 16 depicts another example of a pressure sensor that can be used toimplement various techniques of this disclosure. The example of apressure sensor depicted in FIG. 16 can provide an example of anintegrated pressure sensor that can use one or more Fabry-Perot gratingarrangements. Again, an “integrated” pressure sensor can involve placingthe fiber with the appropriate gratings written in the fiber on aguidewire and then completing the sensor once the fiber is positioned onthe wire.

FIG. 16 is an example of a perspective cross-sectional view of anoptical fiber pressure sensor 1600 that can include an optical fiber1602 that can be configured to transmit one or more optical sensingsignals and a temperature compensated Fiber Bragg Grating (FBG)interferometer 1604 in optical communication with the optical fiber1602. The FBG interferometer 1604 can be configured to receive pressure,e.g., from pressure waves, and to modulate, in response to the receivedpressure, the optical sensing signal. The pressure sensor 1600 caninclude a sensor membrane 1606 that can be in physical communicationwith the FBG interferometer 1604. The sensor membrane 1606 can beconfigured to transmit the pressure to the FBG interferometer 1604.

The example of a pressure sensor 1600 of FIG. 16 can further includeFabry-Perot gratings FBG 1 and FBG 2, which can be used to sense changesin pressure. The Fabry-Perot gratings FBG 1 and FBG 2 can create a phaseshift that can be tracked in a manner similar to that described above.

The pressure sensor 1600 of FIG. 16 can further include a proximal coil1608 and a distal coil 1610. The proximal and distal coils 1608, 1610can provide flexibility to aid advancement of the pressure sensor 1600through tortuous pathways. In one example, the proximal and distal coils1608, 1610 can be affixed together via a mechanical joint (notdepicted), e.g., via solder or adhesive. The proximal end of theproximal coil may be affixed to the core wire by welding, brazing,soldering or via an adhesive. The joint between the proximal and distalcoils may or may not include an attachment between the coils and thecore wire inside the two coils. The FBG interferometer 1604 can, in someexamples, be positioned underneath the mechanical joint to provideadditional protection to the FBG interferometer 1604.

In another example, the proximal and distal coils 1608 and 1610 can becoiled after the two wires that are be used to form the proximal anddistal coils have been joined together to form a coil subassembly,thereby reducing or eliminating any need for another material to affixthe two coils to each other. Low power fiber lasers with typical powerlevels of about 100 W to 200 W average and high beam quality can providethe very small spot sizes needed for this type of precision metalwelding.

The pressure sensor 1600 of FIG. 16 can further include a guidewire 1612to which the optical fiber 1602 can be attached. In the example depictedin FIG. 16, a portion of the guidewire 1612 can define a machined gap(not depicted) underneath the proximal coil 1608. The machined gap canallow the optical fiber 1602 to extend longitudinally or helically alongthe outer surface of the guidewire 1612 and then transition underneaththe proximal coil gradually into the machined gap.

The guidewire 1612 can also define cavity 1614, e.g., filled with air,laterally below the sensor membrane 1606. The sensor membrane 1606 andthe cavity 1614 can concentrate a stress in the area between theFabry-Perot gratings FBG 1 and FBG 2, which can enhance the sensitivityof the pressure sensor 1600. The optical fiber 1602 can be securelyattached to the guidewire 1612 on each side of the cavity 1614. Inaddition, the sensor membrane 1606 can be sealed 360 degrees around theguidewire 1612 at an optical fiber entry end 1616 of the sensor membrane1606 and at a distal end 1618 of the optical fiber 1602 and along theedges of the membrane 1606.

FIG. 17 depicts another example of a pressure sensor that can be used toimplement various techniques of this disclosure. FIG. 17 depicts anotherexample of a pressure sensor that can be used to implement varioustechniques of this disclosure. The example of a pressure sensor 1700depicted in FIG. 17 can provide an example standalone pressure sensorthat can use one or more Fabry-Perot grating arrangements.

FIG. 17 is an example of a perspective cross-sectional view of anoptical fiber pressure sensor 1700 that can include an optical fiber1702 that can be configured to transmit one or more optical sensingsignals and a temperature compensated Fiber Bragg Grating (FBG)interferometer 1704 in optical communication with the optical fiber1702. The FBG interferometer 1704 can be configured to receive pressure,e.g., from pressure waves, and to modulate, in response to the receivedpressure, the optical sensing signal. The pressure sensor 1700 caninclude a sensor membrane 1706 that can be in physical communicationwith the FBG interferometer 1704. The sensor membrane 1706 can beconfigured to transmit the pressure to the FBG interferometer 1704.

The example of a pressure sensor 1700 of FIG. 17 can include four FBGs(e.g., FBGs 1-4.) FBGs 3 and 4 can form a phase-shifted FBG structure,such as for sensing temperature. The change in phase-shift between FBG 3and FBG 4 can be detected and quantified, and the change in temperaturecan be determined from the quantified phase-shift, such as describedabove.

The pressure sensor 1700 can further include Fabry-Perot gratings FBG 1and FBG 2, which can be used to sense changes in pressure. Similar tothe phase-shift grating structures described above with respect to FIG.10D, the Fabry-Perot gratings FBG 1 and FBG 2 can create a phase shiftthat can be tracked in a manner similar to that described above. Thatis, a notch can be created in the wavelength response to the Fabry-Perotgratings FBG 1 and FBG 2, as shown and described in detail above. Apoint on a slope of the notch can be set and tracked, a phase shift canbe detected and quantified, and the change in pressure can be determinedfrom the quantified phase-shift, such as described in detail above.

The pressure sensor 1700 of FIG. 17 can further include a proximal coil1708 and a distal coil 1710. The proximal and distal coils 1708, 1710can provide additional flexibility to aid advancement of the pressuresensor 1700 through tortuous pathways. In one example, the proximal anddistal coils 1708, 1710 can be affixed together via a mechanical joint1712, e.g., via solder or adhesive. The FBG interferometer 1704 can, insome examples, be positioned underneath the mechanical joint 1712 toprovide additional protection to the FBG interferometer 1704.

The pressure sensor 1700 of FIG. 17 can further include a guidewire 1714to which the FBG interferometer 1704 can be attached. In the exampledepicted in FIG. 17, a portion of the guidewire can define a machinedgap 1716 underneath a portion of the proximal coil 1708 and the distalcoil 1710. The machined gap 1716 can allow the optical fiber 1702 toextend longitudinally or helically along the outer surface of theguidewire 1714 and then transition underneath the proximal coil 1708gradually into the machined gap 1716.

The example of a pressure sensor 1700 in FIG. 17 can include acantilevered design, which can be applied to any of the examples ofstandalone pressure sensors described in this disclosure. Moreparticularly, the pressure sensor 1700 can include a cantilever tube1718 that is disposed about a distal portion of the optical fiber 1702within the machined gap 1716. In addition, the pressure sensor 1700 caninclude a sensor tube 1720 disposed within the cantilever tube 1718 andabout the distal portion of the optical fiber 1702. To provide supportto a portion of the optical fiber 1702, the pressure sensor 1700 canalso include a fiber support 1722 that is positioned between the sensortube 1720 and a portion of the optical fiber 1702.

Between a portion of an inner surface of the cantilever tube 1718 and anouter surface of the sensor tube 1720, the pressure sensor 1700 candefine a space 1724, thereby providing a double-walled housingconstruction. The double-walled housing construction and the space 1724can allow the outer surface of the sensor tube 1720 to be mounted to theguidewire 1714 while isolating the FBG interferometer 1704 from motionof the guidewire 1714 and contact with the proximal coil 1708.

The FBG interferometer 1704 can also define cavity 1726, e.g., filledwith air, laterally below the sensor membrane 1706 and a portion of theoptical fiber 1702 and within the region defined by the sensor tube1720. The sensor membrane 1706 and the cavity 1726 can concentrate astress in the area between the Fabry-Perot gratings FBG 1 and FBG 2,which can enhance the sensitivity of the pressure sensor 1700.

FIG. 18 depicts another example of a pressure sensor that can be used toimplement various techniques of this disclosure. The example of apressure sensor depicted in FIG. 18 can provide an example of anintegrated pressure sensor that can use one or more Fabry-Perot gratingarrangements.

FIG. 18 is an example of a perspective cross-sectional view of anoptical fiber pressure sensor 1800 that can include an optical fiber1802 that can be configured to transmit one or more optical sensingsignals and a temperature compensated Fiber Bragg Grating (FBG)interferometer 1804 in optical communication with the optical fiber1802. The FBG interferometer 1804 can be configured to receive pressure,e.g., from pressure waves, and to modulate, in response to the receivedpressure, the optical sensing signal. The pressure sensor 1800 caninclude a sensor membrane 1806 that can be in physical communicationwith the FBG interferometer 1804. The sensor membrane 1806 can beconfigured to transmit the pressure to the FBG interferometer 1804.

The pressure sensor 1800 of FIG. 18 can further include a proximal coil1808 and a distal coil 1810. The proximal and distal coils 1808, 1810can provide additional flexibility to aid advancement of the pressuresensor 1800 through tortuous pathways. In one example, the proximal anddistal coils 1808, 1810 can be affixed together via a mechanical joint1812, e.g., via solder or adhesive. The FBG interferometer 1804 can, insome examples, be positioned underneath the mechanical joint 1812 toprovide additional protection to the FBG interferometer 1804.

The pressure sensor 1800 of FIG. 18 can further include a guidewire 1814to which the FBG interferometer 1804 can be attached. In the exampledepicted in FIG. 18, a portion of the guidewire 1814 can define amachined gap 1816 underneath a portion of the proximal coil 1808 and thedistal coil 1810. The machined gap 1816 can allow the optical fiber 1802to extend longitudinally or helically along the outer surface of theguidewire 1814 and then transition underneath the proximal coil 1808gradually into the machined gap 1816.

The example of a pressure sensor 1800 in FIG. 18 can include a capillarytube design. More particularly, the pressure sensor 1800 can include acapillary tube 1818 to support a portion of the optical fiber 1802. Thecapillary tube 1818 can be disposed about a distal portion of theoptical fiber 1802 within the machined gap 1816.

As seen in FIG. 18, a portion 1817 of the optical fiber 1802 can extendbeyond a distal end of the capillary tube 1818 and over a cavity 1820,e.g., filled with air, that is laterally below the portion of theoptical fiber 1802 that extends beyond the distal end of the capillarytube 1818. The example of a pressure sensor 1800 of FIG. 18 can includeat least three FBGs (e.g., FBGs 1-3.) FBG 1 can be configured to beindependent of pressure and can be used for temperature measurement,such as to provide a temperature compensated optical fiber pressuresensor, such as described above with respect to FIG. 3 and FIG. 4A.

FBGs 2 and 3 can form a phase-shift FBG structure. The surface area ofthe membrane 1806 can concentrate a change in pressure and can focus amechanical response to the change in pressure at the phase-shift regionbetween FBG 2 and FBG 3. This focused mechanical response can enhancethe sensitivity of the pressure sensor 1800. The mechanical forcesacting upon the phase-shift region between FBG 2 and FBG 3 canconcentrate a stress in the phase-shift region. The concentrated stressin the phase-shift region can change the refractive index of the opticalfiber 1802, which, in turn, alters the phase relationship between FBG 2and FBG 3. The change in phase-shift between FBG 2 and FBG 3 can bedetected and quantified, and the change in pressure can be determinedfrom the quantified phase-shift.

As seen in FIG. 18, the sensor membrane 1806 can be disposed about theguidewire 1814, the capillary tube 1818, and the portion of the opticalfiber that extends beyond the distal end of the capillary tube 1818.

FIG. 19 depicts another example of a pressure sensor that can be used toimplement various techniques of this disclosure. FIG. 19 depicts anotherexample of a pressure sensor that can be used to implement varioustechniques of this disclosure. The example of a pressure sensor 1900depicted in FIG. 19 can provide an example standalone pressure sensorthat can use one or more Fabry-Perot grating arrangements.

FIG. 19 is an example of a perspective cross-sectional view of anoptical fiber pressure sensor 1900 that can include an optical fiber1902 that can be configured to transmit one or more optical sensingsignals and a temperature compensated Fiber Bragg Grating (FBG)interferometer 1904 in optical communication with the optical fiber1902. The FBG interferometer 1904 can be configured to receive pressure,e.g., from pressure waves, and to modulate, in response to the receivedpressure, the optical sensing signal.

The example of a pressure sensor 1900 of FIG. 19 can include four FBGs(e.g., FBGs 1-4.) FBGs 3 and 4 can form a phase-shifted FBG structure,such as for sensing temperature. The change in phase-shift between FBG 3and FBG 4 can be detected and quantified, and the change in temperaturecan be determined from the quantified phase-shift, such as describedabove.

The pressure sensor 1900 can further include Fabry-Perot gratings FBG 1and FBG 2, which can be used to sense changes in pressure. Similar tothe phase-shift grating structures described above with respect to FIG.10D, the Fabry-Perot gratings FBG 1 and FBG 2 can create a phase shiftthat can be tracked in a manner similar to that described above. Thatis, a notch can be created in the wavelength response to the Fabry-Perotgratings FBG 1 and FBG 2, as shown and described in detail above. Apoint on a slope of the notch can be set and tracked, a phase shift canbe detected and quantified, and the change in pressure can be determinedfrom the quantified phase-shift, such as described in detail above.

The pressure sensor 1900 of FIG. 19 can further include a proximal coil1906, a distal coil 1908, and a guidewire 1910. The proximal and distalcoils 1906, 1908 can provide additional flexibility to aid advancementof the pressure sensor 1900 through tortuous pathways.

The pressure sensor 1900 of FIG. 19 can further include a tubularhousing 1912 that can be disposed about the guidewire 1912 between theproximal and distal coils 1906, 1908. In one example, the proximal anddistal coils 1906, 1908 can be affixed to the housing 1912 viamechanical joints 1914A, 1914B, e.g., via solder or adhesive. Thehousing 1912 can be affixed to the guidewire 1910 via a mechanical joint1915.

In addition, the pressure sensor 1900 can include a sensor tube 1916disposed within the housing 1912 and disposed about a distal portion ofthe optical fiber 1902. More particularly, the sensor tube 1916 can bepositioned within an area machined out of a portion of the outer wall1918 of the housing 1912. To provide support to the optical fiber 1902,a fiber support 1920 can be disposed about the optical fiber 1902between the sensor tube 1916 and the optical fiber 1902.

To allow the received pressure to reach the optical fiber 1902, aportion of the sensor tube 1916 can be removed in order to define asensor window 1922. The sensor window 1922 can be covered with thesensor membrane 1924.

The example of a pressure sensor 1900 of FIG. 19 can include four FBGs(e.g., FBGs 1-4). FBGs 3 and 4 can form a phase-shifted FBG structure,such as for sensing temperature. The change in phase-shift between FBG 3and FBG 4 can be detected and quantified, and the change in temperaturecan be determined from the quantified phase-shift, such as describedabove.

The pressure sensor 1900 can further include Fabry-Perot gratings FBG 1and FBG 2, which can be used to sense changes in pressure. TheFabry-Perot gratings FBG 1 and FBG 2 can create a phase shift that canbe tracked in a manner similar to that described above. That is, a notchcan be created in the wavelength response to the Fabry-Perot gratingsFBG 1 and FBG 2, as shown and described in detail above. A point on aslope of the notch can be set and tracked, a phase shift can be detectedand quantified, and the change in pressure can be determined from thequantified phase-shift, such as described in detail above.

The pressure sensor 1900 can define a cavity 1926, e.g., filled withair, laterally below the sensor membrane 1924 and the optical fiber1902. The sensor membrane 1924 and the cavity 1926 can concentrate astress in the area between the Fabry-Perot gratings FBG 1 and FBG 2,which can enhance the sensitivity of the pressure sensor 1900.

FIG. 20 depicts another example of a pressure sensor that can be used toimplement various techniques of this disclosure. FIG. 20 depicts anotherexample of a pressure sensor that can be used to implement varioustechniques of this disclosure. The example of a pressure sensor 2000depicted in FIG. 20 can provide an example standalone pressure sensorthat can use one or more Fabry-Perot grating arrangements.

FIG. 20 is an example of a perspective cross-sectional view of anoptical fiber pressure sensor 2000 that can include an optical fiber2002 that can be configured to transmit one or more optical sensingsignals and a temperature compensated Fiber Bragg Grating (FBG)interferometer 2004 in optical communication with the optical fiber2002. The FBG interferometer 2004 can be configured to receive pressure,e.g., from pressure waves, and to modulate, in response to the receivedpressure, the optical sensing signal.

The example of a pressure sensor 2000 of FIG. 20 can include four FBGs(e.g., FBGs 1-4.) FBGs 3 and 4 can form a phase-shifted FBG structure,such as for sensing temperature. The change in phase-shift between FBG 3and FBG 4 can be detected and quantified, and the change in temperaturecan be determined from the quantified phase-shift, such as describedabove.

The pressure sensor 2000 can further include Fabry-Perot gratings FBG 1and FBG 2, which can be used to sense changes in pressure. Similar tothe phase-shift grating structures described above with respect to FIG.10D, the Fabry-Perot gratings FBG 1 and FBG 2 can create a phase shiftthat can be tracked in a manner similar to that described above. Thatis, a notch can be created in the wavelength response to the Fabry-Perotgratings FBG 1 and FBG 2, as shown and described in detail above. Apoint on a slope of the notch can be set and tracked, a phase shift canbe detected and quantified, and the change in pressure can be determinedfrom the quantified phase-shift, such as described in detail above.

The pressure sensor 2000 of FIG. 20 can further include a proximal coil2006, a distal coil 2008, and a guidewire 2010. The proximal and distalcoils 2006, 2008 can provide additional flexibility to aid advancementof the pressure sensor 2000 through tortuous pathways. In one example,the proximal and distal coils 2006, 2008 can be affixed together via amechanical joint 2012, e.g., via solder or adhesive. The FBGinterferometer 2004 can, in some examples, be positioned underneath themechanical joint 2012 to provide additional protection to the FBGinterferometer 2004.

The pressure sensor 2000 of FIG. 20 can further include a tubularhousing 2014 that can be disposed about the guidewire 2010 andunderneath the mechanical joint 2012. The housing 2014 can be affixed tothe guidewire 2010 via a mechanical joint 2015. In addition, thepressure sensor 2000 can include a sensor tube 2016 disposed within thehousing 2014 and disposed about a distal portion of the optical fiber2002. In contrast to the tubular housing of FIG. 19, the tubular housing2014 of FIG. 20 can define a lumen 2018 that extends longitudinallythrough the housing 2014. The sensor tube 2016 of FIG. 20 can bepositioned within the lumen 2018. To provide support to the opticalfiber 2002, a fiber support 2020 can be disposed about the optical fiber2002 between the sensor tube 2016 and the optical fiber 2002.

To allow the received pressure to reach the optical fiber 2002, aportion of the sensor tube 2016 can be removed in order to define asensor window 2022. The sensor window 2022 can be covered with a sensormembrane 2024.

The example of a pressure sensor 2000 of FIG. 20 can include four FBGs(e.g., FBGs 1-4). FBGs 3 and 4 can form a phase-shifted FBG structure,such as for sensing temperature. The change in phase-shift between FBG 3and FBG 4 can be detected and quantified, and the change in temperaturecan be determined from the quantified phase-shift, such as describedabove.

The pressure sensor 2000 can further include Fabry-Perot gratings FBG 1and FBG 2, which can be used to sense changes in pressure. TheFabry-Perot gratings FBG 1 and FBG 2 can create a phase shift that canbe tracked in a manner similar to that described above. That is, a notchcan be created in the wavelength response to the Fabry-Perot gratingsFBG 1 and FBG 2, as shown and described in detail above. A point on aslope of the notch can be set and tracked, a phase shift can be detectedand quantified, and the change in pressure can be determined from thequantified phase-shift, such as described in detail above.

The pressure sensor 2000 can define a cavity 2026, e.g., filled withair, laterally below the sensor membrane 2024 and the optical fiber2002. The sensor membrane 2024 and the cavity 2026 can concentrate astress in the area between the Fabry-Perot gratings FBG 1 and FBG 2,which can enhance the sensitivity of the pressure sensor 2000.

FIGS. 21A-21G depict various examples of a guidewire in combination withan optical fiber pressure sensor. FIG. 21A is an example of a partialcutaway view illustrating a combination 2100 of a guidewire 2102 and anoptical fiber 2104 attached to an optical fiber pressure sensor 2106(FIG. 21C).

In one example, the guidewire 2102 can be substantially similar to theguidewire shown and described in U.S. Pat. No. 5,341,818 to Abrams etal. and assigned to Abbott Cardiovascular Systems, Inc. of Santa Clara,Calif., the entire contents of which being incorporated herein byreference. The guidewire 2102 can include a proximal portion 2108 and adistal portion 2110. The distal portion 2110 can be formed at leastpartially of superelastic materials. The guidewire 2102 can furtherinclude a tubular connector 2112 that can connect a distal end 2114 ofthe proximal portion 2108 and a proximal end 2116 of the distal portion2110.

The tubular connector 2112 joining the proximal portion 2108 and thedistal portion 2110 of the wire may be stainless steel (such as 304series stainless steel) or nitinol material and may be grooved orslotted to accommodate the fiber. The groove or slot in the tubularconnector 2112 may be aligned to the centerline of the tubular connector2112 or it may be angled across the tubular connector 2112 to match thehelix angle of the fiber groove path along the proximal or distalportions of the wire. The wire ends and the tubular connector 2112 maybe adhesively joined, braze or solder attached to each other, thecoupler may be welded to the wire end, or the tubular connector 2112 maybe swaged or crimped onto the wire end.

In the case of a nitinol connector 2112, the connector 2112 can beexpanded mechanically or by cooling it to martensite phase and deformingit. Once the nitinol connector 2112 has been expanded it can beinstalled over the wire and allowed to return to austenite phase,causing it to clamp down on the wire end. FIG. 21E depicts a perspectiveview of an example of a connector 2112.

The guidewire core material can affect the flexibility, support,steering and trackability of the guidewire while the guidewire corediameter can influence the flexibility, support, and torque of theguidewire. Suitable guidewire core materials can include the 18-8stainless steels such as 304V, 304LV, and other 300 series alloys,nickel-based super alloys (such as, for example, MP35N), cobalt chromiummolybdenum based super alloys, and nitinol.

Some examples of suitable metals and metal alloys that can be used toconstruct a guidewire include 304L and 316LV stainless steel; mildsteel; nickel-titanium alloy such as linear-elastic and/or super-elasticnitinol; other nickel alloys such as nickel-chromium-molybdenum alloys(e.g., UNS: N06625 such as INCONEL® 625, UNS: N06022 such as HASTELLOY®UNS: N10276 such as HASTELLOY® C276®, other HASTELLOY® alloys, and thelike), nickel-copper alloys (e.g., UNS: N04400 such as MONEL® 400,NICKELVAC® 400, NICORROS® 400, and the like),nickel-cobalt-chromium-molybdenum alloys (e.g., UNS: R30035 such asMP35-N® and the like), nickel-molybdenum alloys (e.g., UNS: N10665 suchas HASTELLOY® ALLOY B2®), other nickel-chromium alloys, othernickel-molybdenum alloys, other nickel-cobalt alloys, other nickel-ironalloys, other nickel-copper alloys, other nickel-tungsten or tungstenalloys, and the like; cobalt-chromium alloys; cobalt-chromium-molybdenumalloys (e.g., UNS: R30003 such as ELGILOY®, PHYNOX®, and the like);platinum enriched stainless steel; titanium; combinations thereof; andthe like; or any other suitable material. Stainless steel and superalloymaterials provide excellent support, transmission of push force andtorque characteristics but can be less flexible and more susceptible tokinking than nitinol. Nitinol can provide excellent flexibility andsteering but can be less torqueable than stainless steel.

The guidewire core metal alloy materials can be subjected tothermomechanical processing to achieve the desired mechanicalproperties. To achieve the spring temper and ultimate tensile strength(for example, of greater than 300 ksi) desirable for the guidewireproximal shaft, the austenitic stainless steel 304V can be significantlycold worked (e.g. between 93 and 95% cold worked for UTS of 316 to 334ksi). In wire form, 304V can gain tensile strength when stress relievedunder a reducing atmosphere between 350 and 427 degrees Celsius. Nitinolwire can be cold worked (typically between 10 and 75%) during drawingand the amount of cold work in the wire prior to its final heattreatment (or shape set anneal) can dictate the ultimate tensilestrength of the nitinol wire. The final heat treatment (or shape setanneal) for guidewires can be a straightening process performed undercontrolled time, temperature, and pressure conditions. The wire can beheat treated well above the austenite to martensite transformationtemperature (450 to 600 C) while being subjected to longitudinalstresses to impart a straight memory to the wire. The shape set annealprocess can define the final mechanical properties of the wire such asan ultimate yield strength of greater than 155 ksi.

Coupling different materials together to provide the best properties foreach guidewire region can be a significant reason for choosing to joindifferent wire sections together. The present inventors have alsorecognized that coupling different diameter wires together, whetherthose wires are the same material or different materials, can beadvantageous. When the fiber groove is formed during the fiber drawprocessing or by other means into a constant diameter wire, couplingtogether two dissimilar diameter grooved wires can maintain the fibergroove sized appropriately for the fiber as the wire diameter isincreased or decreased. An example is shown in FIG. 21F where a proximalconnector 2113 joins a larger diameter stainless steel proximal shaft2150 to a smaller diameter nitinol intermediate portion 2152 and adistal connector 2112 joins a small diameter stainless steel distalportion 2154 to the nitinol intermediate wire 2152.

In another example, when there is only a single joint between theproximal stainless steel shaft and a distal superelastic nitinol sectionthat extends all the way to the distal tip, it can be desirable toeither leave the region of the shapeable tip in the cold-worked oras-drawn condition so that shaping or permanent deformation of thatregion is possible when the physician intends to form the tip or toeliminate the superelasticity in the shapeable tip region by reversingthe final strain anneal.

The coupled wire joints can be welded together rather than joinedtogether using a tubular connector. This is relatively straightforwardif the two wires are the same material but if they are dissimilarmaterials it is significantly more challenging. A laser based joiningprocess can be used to directly melt the two wires to be joined or tomelt a filler material at the joint. It can be desirable to optimizejoints of stainless steel to nitinol to avoid the intermetallic phaserich in iron and titanium because Fe2Ti is a brittle intermetallic. Anickel or tantalum interlayer between the stainless steel and nitinolcan be used to facilitate a laser weld join between these two materials.

Another laser joining process designed to form joints that aresignificantly smaller than the laser beam spot size can take advantageof heat accumulation at the joint interface. Laser irradiating one ofthe base materials (for example, the nitinol wire) and scanning towardthe nitinol stainless steel interface with a laser power and speed suchthat the equilibrium temperature of the irradiated piece does not exceedits melt temperature (controlling the Gaussian laser spot to be the samediameter as the wires to be joined). Heat accumulation due to thethermal resistance of the interface can cause the temperature to riseabove the melt temp of the nitinol as the laser beam approaches theinterface, forming a molten layer. The laser beam can be turned off asit reaches the interface and the melt layer is quenched when it comes incontact with the adjacent cold work piece to form a seamless braze-likejoint.

Combining a PTFE coated stainless steel proximal shaft with asuperelastic nitinol distal portion via a tube coupler as described byFIGS. 21A, 21E, and 21F and their associated descriptions (or bydirectly joining the stainless steel shaft to the superelastic nitinoldistal end) and employing the polymer sleeve or jacket as describedabove over the distal nitinol portion proximal of a cavity 2162containing the sensor 2106 results in the optical fiber pressure sensorguidewire shown in FIG. 21G. The polymer sleeve or jacket 2160 can becoated with a durable hydrophilic coating, an intermediate coil can bedeployed over the 2162 with an uncoated radiopaque coil over thecorewire distal of the cavity 2162 and sensor 2106. This guidewiresensor assembly 2164 can have the mechanical performance of a secondgeneration high torque frontline guidewire with pressure sensingcapability.

In some example configurations, the fiber pressure sensor assembly caninclude a flexible polymer jacket or sleeve over the tapered distal endof the guidewire core. As used in this disclosure, the term polymer, asused with regard to polymer coatings, is intended to be interpretedbroadly and can include all polymers, prepolymers and the like that aresuitable for use as a coating of a fiber pressure sensor assembly. Anon-limiting list of suitable materials can include polyurethanes,including polyurethane thermoplastic elastomers; polyamides (nylons);polyethers; polyesters; polyacetals; acrylics; methacrylics;cellulosics; fluoropolastics; epoxies; keton-based resins and polymers;polyimide based resins and polymers; bismaleimides; nitriles;polyarylates; polycarbonates; liquid crystal polymers; terephthalateresins and polymers including polybutylene terephthalate andpolyethylene terephthalate; polyetherimides; polyolefins includingpolyethylenes, polypropylenes, polybutylenes, polybutadienes; polyvinylsincluding polystyrenes and polyvinyl chlorides; elastomers especiallythermoplastic elastomers; silicones; rubbers; ionomers; ceramers;dendritic polymers; and derivatives, copolymers, multipolymers, blendsand/or mixtures of any of the previous listed resins and polymers withineach group and between each group, the latter including polyether blockamide elastomers such as COPA and PEBAX.

The polymer sleeve or jacket covering the guidewire core between theproximal shaft the distal coil can provide a smoother surface andtherefore greater lubricity than would a proximal coil disposed overthat section, thereby allowing for smoother tracking through tortuousvasculature. The polymer sleeve or jacket may also be coated with, forexample, a hydrophilic coating. The polymer sleeve or jacket may alsocover coils, leaving the distal coil exposed provides better tactilefeedback. The optical fiber may be positioned under (or within the wallthickness) the polymer sleeve or jacket as was described for routing theoptical fiber along the pressure sensor assembly length covered by aproximal coil or a slotted flexible tube. Alternatively, a groove may becreated (for example by lasing, by various mechanical means includingscribing, a hot wire, etc. or depending on the polymer by thermallysoftening the sleeve or jacket as the fiber is wrapped into place) inthe polymer sleeve or jacket to accommodate the fiber. The guidewire2102 can further include a core wire 2118 having an elongated portion2120 and a tapered portion 2122 extending distally beyond the elongatedportion 2120. In addition, the guidewire 2102 can include a proximalcoil 2124 disposed about the elongated portion 2120 and a distal coil2126 disposed about a portion of each of the elongated portion 2120 andthe tapered portion 2122 and extending distally beyond the taperedportion 2122. The proximal coil 2124 and the distal coil 2126 can bejoined together via a mechanical joint 2128, e.g., solder or adhesive.The guidewire 2102 can further include a distal plug 2130, about which aportion of the distal coil 2126 can be wound, or a conventional soldertip. Additional information regarding the components and construction ofthe guidewire 2102 can be found in U.S. Pat. No. 5,341,818.

Regarding construction of the combination 2100 of the guidewire 2102 andthe optical fiber 2104 attached to an optical fiber pressure sensor 2106(FIG. 21C), in one example, a narrow, shallow channel or groove 2132(FIG. 21B) can be cut into the outer wall of the components that formthe guidewire 2102, e.g., the core wire 2118 and the tubular connector2112. The optical fiber 2104 can be positioned within the groove 2132.Due to the relatively small dimensions of optical fiber 2104, thedimensions of the groove 2132 can have minimal impact on the performanceof the guidewire 2102.

The groove 2132 can extend along the length of the guidewire 2102substantially parallel to a longitudinal axis of the guidewire 2102. Inanother example, the groove 2132 can spiral about the guidewire 2102,e.g., a helically axially extending groove. In other examples, thegroove 2132 can extend along a portion of the length of the guidewire2102 substantially parallel to a longitudinal axis of the guidewire 2102and then the groove 2132 can spiral about another portion of the lengthof the guidewire 2102, e.g., a helically axially extending groove. Thepitch of the spiral can be varied along the length of the guidewire.

The groove 2132 can be fabricated using various techniques that include,but are not limited to, etching, machining, and laser ablation. Inaddition, the groove 2132 can be fabricated at various stages during theconstruction of the guidewire 2102, e.g., before or after applying acoating to the guidewire 2102.

The optical fiber 2104 can be bonded to the groove 2132 using varioustechniques. For example, the optical fiber 2104 can be bonded to thegroove 2132 by applying a hot melt adhesive to the optical fiber 2104prior to positioning the optical fiber 2104 in the groove 2132 and thensubsequently applying heat.

In other examples, rather than a groove 2132 that is cut into the outerwall of the components that form the guidewire 2102, the guidewire 2102can define a lumen (not depicted) that extends along a portion of thelength of the guidewire 2102 substantially parallel to a longitudinalaxis of the guidewire 2102. The lumen can be coaxial with thelongitudinal axis of the guidewire 2102, or the lumen can be radiallyoffset from the longitudinal axis of the guidewire 2102. The opticalfiber 2104 can extend along the length of the guidewire 2102 through thelumen. The dimensions of the lumen can have minimal impact on theperformance of the guidewire 2102.

In another example, the guidewire 2102 can be constructed to include anannular gap (not depicted) between the proximal coil 2124 and theelongated portion 2120. The optical fiber 2104 can then extend along thelength of the elongated portion 2120 between an outer surface of theelongated portion 2120 and an inner surface of the proximal coil 2124.The optical fiber 2104 can be wound about the elongated portion 2120. Insome examples, the optical fiber 2104 can be secured to the elongatedportion 2120, e.g., via an adhesive.

FIG. 21B is an example of a cross-sectional view of the combination 2100of FIG. 21A, such as taken along section B-B of FIG. 21A. The guidewire2102, e.g., a solid guidewire, can include the fabricated groove 2132.FIG. 21B illustrates the optical fiber 2104 positioned within the groove2132 of the core wire 2118 of the guidewire 2102.

FIG. 21C is an example of a cross-sectional view of the combination 2100of FIG. 21A, such as taken along section E-E of FIG. 21A. Moreparticularly, FIG. 21C depicts another example of a pressure sensor 2106that can be used to implement various techniques of this disclosure.

The optical fiber pressure sensor 2106 can include the optical fiber2104 that can be configured to transmit one or more optical sensingsignals and a temperature compensated Fiber Bragg Grating (FBG)interferometer 2134 in optical communication with the optical fiber2104. The FBG interferometer 2134 can be configured to receive pressure,e.g., from pressure waves, and to modulate, in response to the receivedpressure, the optical sensing signal.

The example of a pressure sensor 2106 of FIG. 21C can further includeFBGs (not depicted) similar to those described in detail above withrespect to various examples of pressure sensors, e.g., FIG. 10D, whichcan be used to sense changes in pressure. The FBGs can create a phaseshift that can be tracked in a manner similar to that described above.

The pressure sensor 2106 of FIG. 21C can further include the proximalcoil 2124 and the distal coil 2126. The proximal and distal coils 2124,2126 can provide flexibility to aid advancement of the pressure sensor2106 through tortuous pathways. In one example, the proximal and distalcoils 2124, 2126 can be affixed together via a mechanical joint 2136.The FBG interferometer 2134 can, in some examples, be positionedunderneath the mechanical joint 2136 to provide additional protection tothe FBG interferometer 2134.

As indicated above, the guidewire 2102 can be fabricated with a groove2132 (FIG. 21B) to which the optical fiber 2104 can be attached. Aportion of the optical fiber 2104 can extend underneath the mechanicaljoint 2136. To allow the received pressure to reach the optical fiber2104, a portion of the mechanical joint 2136 can be removed in order todefine a sensor window, shown generally at 2138.

The sensor window 2138 can be covered with the sensor membrane 2140.

In the example depicted in FIG. 21C, the pressure sensor 2106 can beconstructed by fabricating a small cavity 2142 in the core wire 2118that is in communication with the groove 2132 at the distal end of theoptical fiber 2104. The cavity 2142 can, for example, be 100 microns indiameter by 100 microns in depth. The guidewire 2102 can be constructedof the superelastic material, or a different super stiff material may besubstituted at this location (not depicted), for example, aluminum oxide(Al₂O₃) or Alumina ceramic which can be precision molded to define thecavity 2142 and the groove 2132.

The pressure sensor 2106 can further include a microballoon 2144 placedinto the cavity 2142. In some examples, an adhesive (not depicted) canbe placed in the cavity 2142 to secure the microballoon 2144 in place.The microballoon 2144 can be filled with a gas, sealed, and heatexpanded such that, when expanded, the microballoon 2144 can fill thecavity 2142 and maintain a sealed reference chamber. If an upper surfaceof the microballoon 2144 is constricted during its expansion, a flatdiaphragm can be achieved. The optical fiber 2104 with FBGs can bepositioned in the groove 2132 and across the flat diaphragm of themicroballoon 2144.

The remaining space of the cavity 2142 and the groove 2132 can be filledwith an adhesive (not depicted) such as silicone to capture the opticalfiber 2104, to attach the optical fiber 2104 to the guidewire 2102, toattach the optical fiber 2104 to the microballoon 2144, and to define arelatively thin silicone diaphragm in mechanical communication with thechamber defined by the microballoon 2144 where the optical fiber 2104 isembedded. As a pressure is applied, each of the silicone, the opticalfiber 2104, and the microballoon 2144 can flex due to compression of thesealed chamber. The flexing can transmit the received pressure to theFBG interferometer 2134, which can create a responsive phase shiftbetween FBGs (not depicted) that can be tracked in a manner similar tothat described above.

FIG. 21D is an example of a cross-sectional view of the combination 2100of FIG. 21A, such as taken along section A-A of FIG. 21A. Moreparticularly, FIG. 21D depicts a cross-sectional view of the pressuresensor 2106 of FIG. 21C. As seen in FIG. 21D and as described above withrespect to FIG. 21C, the pressure sensor 2106 of FIG. 21C can includethe microballoon 2144 positioned within the cavity 2142. The opticalfiber 2104 with FBGs can be positioned in the groove 2132 and across theflat diaphragm 2146 of the microballoon 2144.

Any of optical fiber pressure sensors described in this disclosure canbe combined with the guidewire 2102 shown and described above withrespect to FIG. 21A and in U.S. Pat. No. 5,341,818. Further, thetechniques of this disclosure are not limited to the use of a singlesensor in combination with a guidewire, e.g., guidewire 2102. Rather,two or more sensors, e.g., pressure sensors, can be combined with aguidewire by defining sensor regions in which each of the two or moresensors can function at a respective, unique wavelength and can beaddressed accordingly by a laser matching the wavelength of therespective sensor. Each laser can be multiplexed onto the optical fiberusing standard techniques, e.g., wavelength-division multiplexing (WDM),found in telecommunications systems.

By way of example, two pressure sensors can be positioned along thelength of the core wire 2118. One pressure sensor can be located asshown in FIG. 21A. A second sensor can be positioned proximally suchthat it can record the pressure proximal to an obstruction in the bloodvessel. With this example configuration, the guidewire can measure theaortic pressure (Pa) and the distal pressure (Pd), thereby allowing thecomputation of FFR as Pa/Pd without relying on external pressuresensors. This can simplify the configuration of console equipmentinterconnection as the pressure sensor console would not need to beconnected to an external pressure monitoring system.

By way of a further example, the two (or more) pressure sensors can beconfigured using a single fiber with each pressure sensor operating at aunique and separable wavelength. In the case of two sensors, taking theexamples of pressure sensor embodiments detailed herein, such as thosein FIGS. 60 and 61, the proximal sensor can be configured such that thedistal temperature sensing portion can accommodate sufficient slack inthe fiber placement so that the pressure sensor operation would not beimpeded.

In yet another configuration, the incorporation of multiple pressuresensors can be achieved through integration of multiple optical fibersand sensors, each operational at the same wavelength of light oralternatively at more than one wavelength. Multiple optical fibers canbe accommodated in various exemplary ways. The optical fibers can beplaced in close proximity to each other along the length of theguidewire, or the optical fibers can be evenly or unevenly spaced aroundthe circumference of the guidewire, such as in double or multiplehelical formation or other winding patterns, or straight along thelength of the guidewire. To accommodate the multiple optical fibers, thegroove along the length of the guidewire can be widened, or separategrooves can be furnished around the circumference of the guidewire.Alternatively, a larger luminal bore can be made through the guidewirecore.

In another example, the guidewire 2102 of FIG. 21A can be combined withother sensor techniques. For example, the same guidewire can be used forboth intravascular ultrasound (IVUS) imaging and pressure sensing byusing the imaging sensor configurations described in U.S. Pat. No.7,245,789 to Bates et al., and assigned to Vascular Imaging Corp, theentire contents of which being incorporate herein by reference. By wayof specific example, one of the optical fibers in a 32 fiber arrangementcan extend distally beyond an imaging sensor region, where an opticalfiber pressure sensor, such as any of the optical fiber pressure sensorsdescribed in this disclosure, can be included that utilizes a differentwavelength than that used by the imaging arrangement.

FIG. 22 depicts an example of a combination 2200 of a guidewire 2202with an optical fiber pressure sensor 2204 and an imaging sensor 2206,e.g., using the imaging sensor configurations described in U.S. Pat. No.7,245,789. In particular, FIG. 22 is an example of a perspective partialcutaway view of the combination 2200.

The guidewire 2202 is similar in construction to the guidewire 2102described above with respect to FIG. 21A, and as shown and described inU.S. Pat. No. 5,341,818. The guidewire 2202 can include a core wire2208, a proximal coil 2210, and a distal coil 2212.

The imaging sensor 2206 can include an optical fiber ribbon 2214 havinga plurality of optical fibers, e.g., 32 optical fibers, disposed aboutthe core wire 2208 of the guidewire 2202, and a plurality of imaginggratings 2216 to couple light into and/or out of one or more respectiveoptical fibers of the ribbon 2214.

The guidewire 2202 can further include a backing 2218 disposed about thecore wire 2208 and positioned between the core wire 2208 and the opticalfiber ribbon 2214. In addition, the guidewire 2202 can include amechanical joint 2220 for joining a proximal portion 2222 of theguidewire 2202 to a distal portion 2224 of the guidewire 2202.

In one example, the pressure sensor 2204 can be similar to the pressuresensor 2106 of FIG. 21C. For purposes of conciseness, the pressuresensor 2204 will not be described in detail again. The pressure sensor2204 can include a single optical fiber 2226 that extends longitudinallyalong the length of the guidewire 2202, e.g., within a groove in theouter surface of the core wire 2208 and underneath the optical fiberribbon 2214. The pressure sensor 2204 can further include a pressuresensing window 2228 and pressure sensor membrane 2230, as described indetail above. The pressure sensor 2204 of FIG. 22 is not limited to thedesign of the pressure sensor 2106 of FIG. 21C. Rather, any of thepressure sensor configurations described in this disclosure can beapplied to the combination 2200.

In one example, an outer diameter of the guidewire 2202 can be reducedalong the length of the guidewire 2202 up to the distal coil 2212 toallow the optical fiber ribbon 2214 to be disposed about the outersurface of the guidewire 2202. By way of specific example, the outerdiameter of the proximal coil 2210 can be reduced from 0.014″ to 0.011″and the pressure sensor 2204 can be incorporated with the guidewire 2202either in a surface groove or a coaxial hole of the core wire 2208. Theoptical fiber ribbon 2214, e.g., a 32 optical fiber arrangement, of theimaging sensor 2206 can then be positioned over the 0.011″ outerdiameter of the guidewire 2202 so that the assembly contains 33 opticalfibers, for example. This configuration can separate the multiplexingrequirements of the imaging sensor 2206 and the pressure sensor 2204,and can allow the pressure sensor 2204 to operate at any wavelength,including that of the imaging sensor 2206.

In another example, the guidewire 2202 of FIG. 22 can be attached to oneor more consoles by way of a connector. The connector can contain the 32or more optical fibers according to the construction of the guidewire2202. For the example where the one or more pressure sensors are formedin the same optical fibers of the imaging sensor(s), the 32 or moreimaging fibers can be attached to a console using, for example, theconnection techniques described in U.S. Pat. No. 8,583,218 to Michael J.Eberle and WIPO Patent Application No. WO 2014/159702 to Tasker et al.,the entire content of each incorporated herein by reference.

The console or connecting apparatus can contain circuitry and/or modulesadapted to split or separate the optical signals for pressure sensingand imaging. The signals for imaging can be directed to a control andsignal detection apparatus for subsequent processing into images. Thesignals for pressure sensing can be directed to a control and signaldetection apparatus for processing and conversion into pressure signals.

The functionality of imaging and pressure sensing can be contained in asingle console for display on a single screen or separate screens orother indicators. Alternatively, the imaging and pressure functionalitycan be contained in separate consoles or modules within one or moreconsoles for display on one or more screens. For the example where theone or more pressure sensors are formed on optical fibers separate tothe 32 or more image sensing optical fibers, the separation means may beunnecessary. As illustrated by these and other examples, the combinationguidewire of FIG. 22 can enable simultaneous or serial imaging andpressure sensing capabilities when attached to one or more consoles ormodules. Although the example of a 32 optical imaging fiber coronaryguidewire has been described, the techniques of the current disclosurecan be applied to guidewires containing more or less than 32 opticalfibers, larger guidewires, catheters, smaller or larger optical fibers,various IVUS imaging configurations including various ultrasonicfrequencies and more.

FIGS. 23A-23B depict another example of a guidewire in combination withan optical fiber pressure sensor. FIG. 23A is an example of a partialcutaway view illustrating a combination 2300 of a guidewire 2302 and anoptical fiber 2304 attached to an optical fiber pressure sensor 2306(FIG. 23B).

The guidewire 2302 can include a proximal portion 2308 and a distalportion 2310. The distal portion 2310 can be formed at least partiallyof superelastic materials. The guidewire 2302 can further include atubular connector 2312 that can connect a distal end 2314 of theproximal portion 2308 and a proximal end 2316 of the distal portion2310.

The guidewire 2302 can further include a core wire 2318 having anelongated portion 2320 and a tapered portion 2322 extending distallybeyond the elongated portion 2320. In addition, the guidewire 2302 caninclude a proximal coil 2324 disposed about the elongated portion 2320and the tapered portion 2322. The guidewire 202 can also include adistal coil 2326 disposed about a portion of the tapered portion 2322and extending distally beyond the tapered portion 2322. The proximalcoil 2324 and the distal coil 2326 can be joined together via amechanical joint 2328, e.g., solder or adhesive. The guidewire 2302 canfurther include a distal plug 2330, about which a portion of the distalcoil 2326 can be wound, or a conventional solder tip.

Regarding construction of the combination 2300 of the guidewire 2302 andthe optical fiber 2304 attached to an optical fiber pressure sensor2306, in one example, a narrow, shallow channel or groove (not depicted)can be cut into the outer wall of the components that form the guidewire2302, e.g., the core wire 2318 and the tubular connector 2312. Theoptical fiber 2304 can be positioned within the groove. Due to therelatively small dimensions of optical fiber 2304, the dimensions of thegroove can have minimal impact on the performance of the guidewire 2302.

The groove can extend along the length of the guidewire 2302substantially parallel to a longitudinal axis of the guidewire 2302. Inanother example, the groove can spiral about the guidewire 2302, e.g., ahelically axially extending groove. In other examples, the groove canextend along a portion of the length of the guidewire 2302 substantiallyparallel to a longitudinal axis of the guidewire 2302 and then thegroove can spiral about another portion of the length of the guidewire2302, e.g., a helically axially extending groove. The pitch of thespiral can be varied along the length of the guidewire.

The groove can be fabricated using various techniques that include, butare not limited to, etching, machining, and laser ablation. In addition,the groove can be fabricated at various stages during the constructionof the guidewire 2302, e.g., before or after applying a coating to theguidewire 2302.

The optical fiber 2304 can be bonded to the groove using varioustechniques. For example, the optical fiber 2304 can be bonded to thegroove by applying a hot melt adhesive to the optical fiber 2304 priorto positioning the optical fiber 2304 in the groove and thensubsequently applying heat.

The guidewire 2302 can be constructed to include an annular gap, shownin FIG. 23B at 2332, between the proximal coil 2324 and the portions2320, 2322. The optical fiber 2304 can then extend along the length ofthe portions 2320, 2322 of the distal portion 2310 between an outersurface of the portions and an inner surface of the proximal coil 2324.The optical fiber 2304 can be wound about the elongated portion 2320. Insome examples, the optical fiber 2304 can be secured to the elongatedportion 2320, e.g., via an adhesive.

The combination 2300 can further include a sleeve 2334 disposed aboutthe core wire 2318 and underneath the mechanical joint 2328, to receivea distal portion of the optical fiber 2304. In one example, sleeve 2334can be constructed of aluminum oxide (Al₂O₃), or other stiff material.The core wire 2318 can taper as it extends underneath the mechanicaljoint.

FIG. 23B is an example of a partial cutaway view of a portion of thecombination 2300 of FIG. 23A. More particularly, FIG. 23B depictsanother example of a pressure sensor 2306 that can be used to implementvarious techniques of this disclosure.

The optical fiber pressure sensor 2306 can include the optical fiber2304 that can be configured to transmit one or more optical sensingsignals and a temperature compensated Fiber Bragg Grating (FBG)interferometer 2334 in optical communication with the optical fiber2304. The FBG interferometer 2334 can be configured to receive pressure,e.g., from pressure waves, and to modulate, in response to the receivedpressure, the optical sensing signal.

The example of a pressure sensor 2306 of FIG. 23B can further includeFBGs (not depicted) similar to those described in detail above withrespect to various examples of pressure sensors, e.g., FIG. 10D, whichcan be used to sense changes in pressure. The FBGs can create a phaseshift that can be tracked in a manner similar to that described above.

The pressure sensor 2306 of FIG. 23B can further include the proximalcoil 2324 and the distal coil 2326. The proximal and distal coils 2324,2326 can provide flexibility to aid advancement of the pressure sensor2306 through tortuous pathways. In one example, the proximal and distalcoils 2324, 2326 can be affixed together via a mechanical joint 2328.The FBG interferometer 2334 can, in some examples, be positionedunderneath the mechanical joint 2328 to provide additional protection tothe FBG interferometer 2334.

As indicated above, the guidewire 2302 can be constructed to include anannular gap 2332 between the proximal coil 2324 and the portion 2320 toallow the optical fiber 2304 to extend along the length of the portion2320. The sleeve 2334 can include a lumen, groove, or pocket to receivethe distal end of the optical fiber 2304. To allow the received pressureto reach the optical fiber 2304, a portion of the mechanical joint 2328and the sleeve 2334 can be removed in order to define a sensor window,shown generally at 2338. The sensor window 2338 can be covered with thesensor membrane 2340.

In the example depicted in FIG. 23B, the pressure sensor 2306 can beconstructed by fabricating a small cavity 2342 in the core wire 2318.The cavity 2342 can, for example, be 100 microns in diameter by 100microns in depth. The guidewire 2302 can be constructed of thesuperelastic material, or a different super stiff material may besubstituted at this location (not depicted), for example, Al₂O₃, orAlumina ceramic which can be precision molded to define the cavity 2342.

The pressure sensor 2306 can further include a microballoon 2344 placedinto the cavity 2342. In some examples, an adhesive (not depicted) canbe placed in the cavity 2342 to secure the microballoon 2344 in place.The microballoon 2344 can be filled with a gas, sealed, and heatexpanded such that, when expanded, the microballoon 2344 can fill thecavity 2342 and maintain a sealed reference chamber. If an upper surfaceof the microballoon 2344 is constricted during its expansion, a flatdiaphragm can be achieved. The optical fiber 2304 with FBGs can bepositioned in the sleeve 2334 and across the flat diaphragm of themicroballoon 2344.

As a pressure is applied, the optical fiber 2304 and the microballoon2344 can flex due to compression of the sealed chamber. The flexing cantransmit the received pressure to the FBG interferometer 2334, which cancreate a responsive phase shift between FBGs (not depicted) that can betracked in a manner similar to that described above.

FIG. 24 shows an example of a portion of a concentric pressure sensorassembly 2400. The concentric pressure sensor assembly 2400 can includeor be coupled to an optical fiber 2402, such as a reduced-diameterlongitudinally extending central optical fiber 2402. The concentricpressure sensor assembly 2400 can be located at or near a distal regionof the optical fiber 2402. In an example, the pressure sensor assembly2400 can include at least one Fabry-Perot interferometer, such as in theoptical fiber 2402. The Fabry-Perot interferometer can modulate thewavelength of light in the optical fiber 2402, such as in response toenvironmental pressure variations that can stretch or compress theoptical fiber 2402, e.g., longitudinally and linearly. The modulatedlight in the optical fiber 2402 can be used to communicate informationabout the environmental pressure variations at or near the distal end ofthe optical fiber 2402 to a proximal end of the optical fiber 2402, suchas for coupling the resulting optical signal to an optoelectronic orother optical detector, which, in turn, can be coupled to electronic oroptical signal processing circuitry, such as for extracting orprocessing the information about the sensed environmental pressurevariations.

A distal portion of the optical fiber 2402 (e.g., more distal than theone or more Fabry-Perot interferometers) can be securely captured,anchored, or affixed, such as at a hard, solid, or inelastic distal diskassembly, distal endcap, or other distal anchor 2404, such as can belocated at a distal end portion of the concentric pressure sensorassembly 2400. The hard, solid, or inelastic material (e.g., fusedsilica or other suitable material) of the distal anchor 2404 can berelatively inflexible, e.g., relative to the dimensional variation ofthe optical fiber 2402 in response to the targeted environmentalpressure variations to be measured. In an illustrative example, anydimensional variation of the distal anchor 2404 can be less than orequal to 1/20, 1/100, or 1/1000 of any dimensional variation of apressure-sensing portion of the optical fiber 2402 measured in responseto the targeted environmental pressure variations, such as the pressurevariations that can be present in a percutaneous in vivo intravascularhuman blood pressure sensing application.

The tubular or other distal anchor 2404 can be attached to a hard,solid, or inelastic (e.g., fused silica) tubular or other housing 2406,such as by a soft, flexible, elastic, or compliant gasket 2408 that canbe located therebetween. A first sensing region 2410 of the opticalfiber 2402 can be securely captured, anchored, or affixed, to thehousing 2406, such as via a tubular or other attachment (e.g., hardenedepoxy or other adhesive) region 2412. A second sensing region 2414 ofthe optical fiber 2402 can be located within the housing 2406, such assuspended (e.g., freely or within a compliant material) between theencapsulator or attachment region 2412 and the hard distal anchor 2404.The suspended portion of the optical fiber 2402 can be installed orsecurely held longitudinally under tension. This can permit bothpositive and negative direction longitudinal displacement variations inthe suspended portion of the optical fiber 2402, which, in turn, canpermit sensing of both positive and negative environmental pressurevariations, as explained herein.

The gasket 2408 material (e.g., medical grade silicone) can berelatively more flexible, soft, elastic, or compliant than the housing2406 and than the distal anchor 2404, such as to allow longitudinaldimensional variation of gasket 2408 and the suspended second sensingregion 2414 of the optical fiber 2402 in response to the targetedenvironmental pressure variations to be measured, such as the pressurevariations that can be present in a percutaneous in vivo intravascularhuman blood pressure sensing application. The first sensing region 2410can be securely fixed to the hard housing 2406 by the encapsulator orattachment region 2412, while the second sensing region 2414 can besuspended within the hard housing 2406 and subject to longitudinaldimensional variation (along with longitudinal dimensional variation ofthe compliant gasket 2408). Therefore, the first sensing region 2410 canbe shielded from or made insensitive to environmental pressurevariations, but sensitive to environmental temperature variations, whilethe second sensing region 2414 can be sensitive to both environmentalpressure and temperature variations. In this way, light modulation inthe first sensing region 2410 due to temperature variations can bemeasured and used to compensate for or null-out the light modulationeffect of similar temperature variations experienced by the secondsensing region 2414 that is being used to measure environmental pressurevariations. In an illustrative example, the first sensing region 2410can include a first Fabry-Perot interferometer, and the second sensingregion 2414 can include a second Fabry-Perot interferometer. Theserespective interferometers can be written with different wavelengths.This can permit each interferometer to be individually separatelyaddressed by selecting a corresponding wavelength of light to provide tothe proximal end of the optical fiber 2402 to perform the selectiveindividual addressing of the interferometers.

FIG. 24 can be conceptualized as an arrangement in which at least oneoptical fiber sensing region can be suspended from or between twoanchors (e.g., hard tubes 2404, 2406) that can be separated from eachother by a compliant region (e.g., gasket 2408) that can allow theanchoring tubes 2404, 2406 (and hence the suspended portion of theoptical fiber 2402) to experience longitudinal displacement in responseto environmental pressure variations. Based on finite element modeling(FEM) simulation analysis and experimental laboratory data obtained fromprototypes, corresponding to the arrangement illustrated in FIG. 24, apressure sensitivity can be obtained that can be at least 100 to 150times the pressure sensitivity of an optical fiber without sucharrangement of hard tubes 2404, 2406 separated from each other by thecompliant gasket 2408.

In an illustrative example, the entire pressure sensor assembly 2400 canbe less than or equal to 1.5 millimeters in length, such as less than orequal to 1.0 millimeter in length. The pressure sensor assembly 2400 canhave an outer diameter that can be less than or equal to 125micrometers. For comparison, 125 micrometers is the outer diameter of atypical single standard optical fiber as used in telecommunications. Thetubular housing 2406 can have an inner lumen diameter of about 50micrometers. In an example, the entire pressure sensor assembly 2400 canbe conveniently incorporated within a percutaneous or other guidewire,such as can be used for guiding an intravascular device (e.g., a stent,such as a coronary stent) to a desired location within a blood vessel.For example, the entire pressure sensor assembly 2400 can be includedwithin a solder or other joint of such a guidewire, such as betweenspring coils forming a body of the guidewire. Using fused silica orother glass components for all or portions of the tubular housing 2406or the fused silica distal anchor 2404 can provide components that canprovide a good matching of the temperature coefficient of expansion ofthese materials to the temperature coefficient of expansion of thematerial of the optical fiber 2402.

The arrangement shown in the illustrative example of FIG. 24 canadvantageously be durable, can be easy to make, can perform well such asin detecting and amplifying an environmental pressure variation, or canconsistently be made in a small form factor.

FIG. 25 shows an example of the pressure sensor assembly 2400 as it canbe prefinished and included or otherwise incorporated into apercutaneous intravascular guidewire assembly 2500. The guidewireassembly 2500 can include a core guidewire 2502, a flexible proximalspring coil region 2504 and a flexible distal spring coil region 2506that can terminate at a rounded and atraumatic distal tip. A generallycylindrical or other connector block 2508 can be included between andinterconnecting the proximal spring coil region 2504 and the distalspring coil region 2506. The connector block 2508 can include a reduceddiameter proximal end seat region 2510 and a reduced diameter distal endseat region 2512, about which windings of the flexible proximal springcoil region 2504 and a flexible distal spring coil region 2506 canrespectively be wound, such as with their outer circumferences flushwith an outer circumference of a midportion of the connector block 2508between the proximal end seat region 2510 and the reduced diameterdistal end seat region 2512. The connector block 2508 can provide ahousing for the pressure sensor assembly 2400. The optical fiber 2402can extend proximally from the pressure sensor assembly 2400 in theconnector block 2508 through the proximal spring coil region 2504, suchas to an optical connector at a proximal end of the guidewire assembly2500, where it can be optically coupled to optical, electronic, oroptoelectronic signal generation or processing circuitry. The coreguidewire 2502 of the guidewire assembly 2500 can bend or jog off of theconcentric longitudinal axis of the guidewire assembly 2500, such as ator near the connector block 2508, if needed to allow enough room for thepressure sensor assembly 2500 to be housed within the connector block2508 while also allowing passage of the core guidewire 2502 through theconnector block 2508 in such a lateral offset arrangement.

The connector block 2508 can provide a lateral axis portal 2514 that canbe located beyond a distal end region 2516 of the pressure sensorassembly 2400 such as to leave a distal end region 2516 of the pressuresensor assembly 2400 exposed to nearby environmental pressures to bemeasured, while providing a ceramic or other hard protectivecircumferential housing region that can protect the pressure sensorassembly 2400 from lateral pressure or lateral torque that may otherwiseinfluence the pressure sensor measurement to be obtained by longitudinalspatial variations of the pressure sensor assembly 2400.

FIG. 26 shows an example illustrating how components of the pressuresensor assembly 2400 can be integrated into or otherwise incorporatedinto a percutaneous intravascular guidewire assembly 2600. FIG. 26 issimilar to FIG. 25 in some respects, but in FIG. 26 the connector block2602 can provide a concentric axially aligned longitudinal passage forthe core guidewire 2502, such that it need not bend or jog as shown inFIG. 25. This can help preserve or utilize the mechanical properties orcharacteristics of the core guidewire 2502 or those of the guidewireassembly 2600. One or more components of the pressure sensor assembly2400 can be laterally offset from the concentric axially aligned coreguidewire 2502, such as within the connector block 2602. The connectorblock 2602 can include a lateral axis portal 2514. The distal anchor2404 and the gasket 2408 can be located in or near the lateral axisportal 2514, and can optionally be laterally recessed or otherwiseshielded from lateral pressure or torque that may otherwise influencethe pressure sensor measurement to be obtained by longitudinal spatialvariations of the integrated components of the pressure sensor assembly2400, such as explained above with respect to FIG. 25. The connectorblock 2602 can be constructed with a passage for the optical fiber 2402sized, shaped, or otherwise configured such as to provide a firstsensing region 2410 of the optical fiber 2402 that can be affixed to ahousing provided by the connector block 2602, such as explained herein.A second sensing region 2414 of the optical fiber 2402 can be suspendedwithin a housing provided by the connector block 2602, such as explainedherein. The optical fiber 2402 can extend outward from the connectorblock 2602 proximally, such as through the proximal spring coil region2504, such as with the optical fiber 2402 extending so as to belaterally offset from a longitudinal central axis of the guidewireassembly 2600.

FIG. 27 shows an example in which components of the pressure sensingassembly 2400 can be retrofitted to or otherwise integrated into anexisting guidewire assembly 2700, such as a RUNTHROUGH® guidewire,available from Terumo Kabushiki Kaisha, also known as Terumo Corp. Theguidewire assembly 2700 can include a proximal region 2702, that can beconstructed from a first material, such as stainless steel, and a distalregion 2706 that can be constructed from a second material, such asnitinol. Either or both of the proximal region 2702 and the distalregion 2704 can taper inward in a direction toward the distal end of theguidewire assembly 2700, such as in one or more tapering regions, whichcan be contiguous or separated by respective non-tapering regions. Adistal region 2706 of the guidewire assembly 2700 can include a proximalspring coil region 2504, a distal spring coil region 2506, a connectorblock 2708 (e.g., containing components of the pressure sensor assembly2400, such as described herein) therebetween from which a flattened orother core guidewire can extend distally toward and connecting to anatraumatic rounded distal tip 2710.

At least one groove 2712 can be formed on an outward circumferentialsurface of the guidewire assembly 2700. The groove 2712 can extend froma proximal end or region of the guidewire assembly 2700 toward and to adistal portion of the guidewire assembly 2700 and can terminate at aproximal side of the connector block 2708. The groove 2712 can extendalong all or a portion of the length of the guidewire assembly 2700,such as in a spiral helix or otherwise. The pitch of the helix can befixed or multi-valued (e.g., a looser pitch (e.g., between 30 mm and 50mm) at a proximal portion of the guidewire assembly 2700 and a tighterpitch (e.g., between 5 mm and 10 mm pitch) at the distal (e.g., over alength of about 30 centimeters) portion of the guidewire assembly 2700).The helical arrangement can help accommodate flexing curvature in theguidewire assembly 2700 as it is introduced along tortuous vascular orother non-linear paths. A tighter pitch can be more accommodating tocurvature in the guidewire assembly 2700. The groove 2712 can carry theoptical fiber 2402 therein, such as can be secured therein by anadhesive underlayer (e.g., UV-cured adhesive, hot-melt adhesive, epoxyor other two-part adhesive) or overlayer (e.g., such as any suitableovercoating used for an existing guidewire). In an example, the groove2712 can be about 40 micrometers across and about 40 micrometers deep,and can be constructed so as to only occupy about 1/100 or less of thesurface area of the guidewire assembly 2700, thereby leaving themechanical properties of the guidewire assembly 2700 substantiallyintact as though the groove 2712 were not present. For retrofitting anexisting guidewire, the groove 2712 can be formed by laser-etching orother suitable process. The guidewire can additionally or alternativelyformed together with the groove 2712, such as during drawing of theguidewire body during its manufacture, such as by mechanically scoringthe guidewire body or otherwise. If a portion of the guidewire body istapered down (e.g., toward a distal end, such as using centerless orother grinding), then any grooves that were formed during the guidewiredrawing, but removed by the grinding, can be replaced by a respectiveconnecting groove that can be formed after grinding, such as bylaser-etching the ground portion of the guidewire body.

FIG. 28 shows an example in which the pressure sensor assembly 2400(e.g., as explained herein) can be located at a distal end of aguidewire assembly 2800, e.g., more distal than the distal spring coilregion 2506, such as within or providing a rounded atraumatic distaltip. A flattened or other distal end of the core guidewire 2502 canconnect to a proximal end of the housing 2406 of the pressure sensorassembly 2400. More proximal regions of the guidewire assembly 2800 caninclude a proximal spring coil region 2504, a connector block (such as aconnector block 2508, which can optionally include a second, moreproximal pressure sensor as described with respect to FIG. 25), andother elements such as shown in FIG. 25.

The distal end pressure sensor assembly 2400 can include an anchoredfirst sensing region 2410 and a suspended second sensing region 2414,such as explained herein. The gasket 2408 and the distal anchor 2404 canbe located within a cylindrical or other recess 2802 that can be exposedto the ambient environment about the distal end of the guidewireassembly 2800. In an example such as shown in FIG. 28, the recess 2802can be cylindrical and can extend longitudinally along the central axisof the guidewire assembly 2800, such as to face longitudinally outwardfrom the distal end of the guidewire assembly 2800. In an example, thedistal end of the optical fiber 2402 can be attached to the anchor 2404,and both the anchor 2404 and the gasket 2408 can be suspended within therecess 2802, such as by tension in the optical fiber 2402 to which theanchor 2404 can be attached with the gasket 2408 captured proximal tothe anchor 2404. This can help provide pressure sensing due tolongitudinal optical fiber tension variations near the distal end of theguidewire assembly 2800, and can help isolate the effect of lateralpressure variations or torque upon the pressure sensor assembly 2400.

Having a pressure sensor located at a guidewire distal tip can provideadvantages in certain applications, such as where information aboutpressure distal to an occlusion may be desirable. For example, whenpushing a guidewire across a chronic total vascular occlusion, it may bedifficult to determine whether the distal tip is within a lumen of theblood vessel or within a subintimal layer of the blood vessel. Adistal-tip pressure sensor can permit providing distal-tip pressureinformation that can be useful in determining the nature of suchlocation of the distal tip of the guidewire assembly 2800. In an examplein which a distal tip pressure sensor is provided together with a moreproximal pressure sensor (e.g., located between the proximal spring coilregion 2504 and the distal spring coil region 2506), a pressuredifferential across an occlusion can be sensed and provided to a user,such as for diagnostic or interventional (e.g., stent-placement)purposes.

Guidewires that are used to measure pressure in body lumens, e.g.,coronary arteries, and the derived index of Fractional Flow Reserve(FFR), need to perform their measurement accurately in a challengingenvironment. The proximal end of a steerable guidewire is typicallyhandled by the coronary interventionalist, for example, and is exposedto various contaminants such as blood, contrast fluid and saline. Theinterventionalist is accustomed to keeping the guidewire relativelyclean, by wiping with saline wetted gauze cloths, in order to ensurethat any catheters which are inserted over the wire do not get stuck ordo not introduce emboli into the coronary arteries.

Over the last 15 years, electrical based pressure guidewires have comeinto practice. For these devices, the physician is accustomed to extracare in the region of the disconnectable proximal electricalconnections. Typically a saline wipe as well as a drying step isperformed before the proximal end is inserted into the mating electricalconnector. Contamination or fluids in the electrical connector can leadto unreliable pressure readings.

The present inventors have determined that it can be desirable toimprove the reliability of the proximal optical connection of thecurrent invention and to facilitate the connection process. The presentinventors have determined that it is desirable that the alignmentbetween the cores of the standard fiber and the reduced cladding fiberin the electrical connection be accurate to the order of 1 micrometer tominimize optical losses. This level of accuracy is typically achieved inoptical connectors utilized in the telecommunications industry, howeverthe connectors used would be too expensive to implement and would alsobe too large.

FIG. 29A shows an example of a proximal region of a guidewire assembly2900, such as one of the various guidewire assemblies described herein,terminating at a proximal end connector 2902. The guidewire assembly2900 can include a helically wound optical fiber 2402 that can belocated in a helical groove 2712 along the guidewire body. The proximalend connector 2902 can include separable portions: (1) a distal portionthat can include a metal or other tube 2904 (also referred to as atubular coupler) having an interior lumen diameter that can be attachedto both the outer diameter of the body of the proximal region of theguidewire assembly 2900 and the outer diameter of a ceramic or otherdistal ferrule 2906 such that the optical fiber can extend from aperiphery of the guidewire body to and through a center axis lumen ofthe distal ferrule 2906; and (2) a proximal portion that can include aconnector housing 2908 carrying a ceramic or other proximal ferrule2910, a split sleeve ferrule guide 2912, and a distal receptacle guide2914 that can provide a tapered portion into which a portion of thedistal ferrule 2906 and the metal tube 2904 can be received.

The split sleeve ferrule guide 2912 can be made from ceramic (forexample, zirconia) or metal (for example, nickel, beryllium copper, orphosphor bronze). The fit of the split sleeve ferrule guide 2912 to theferrule 2906 should be sized such that the split opens slightly as theferrule 2906 is inserted into the split sleeve ferrule guide 2912 inorder to hold and locate the ferrule 2906 as accurately as possible. Thesplit sleeve ferrule guide fit to the ferrule is typically based on theforce needed to insert the ferrule 2906 into the split sleeve ferruleguide 2912 and the force needed to withdraw the ferrule 2906 from thesplit sleeve ferrule guide 2912. For these miniaturized connectorcomponents, the ferrule withdrawal force from the split sleeve ferruleguide would ideally be less than 100 grams force and preferably lessthan 70 grams force.

The optical fiber 2402 can terminate at a flat or dome polished (e.g.,ultrapolished physical connector, “UPC”) proximal end of the distalferrule 2906, where it can butt against and optically couple with a flator dome polished (e.g., UPC) distal end of the proximal ferrule 2910,which can provide a center axis lumen through which an optical fiber2402 can extend in a proximal direction, such as to an optical,electronic, or optoelectronic signal generation or processing apparatus.While the optical fibers 2402 and 2916 can be the same diameter, in anexample, the optical fiber 2402 can be a small diameter optical fiber(e.g., 25 micrometers outer diameter) and the optical fiber 2916 can bea standard sized telecommunications optical fiber (e.g., 125 micrometersouter diameter), such as with the mode field diameter (MFD) of theoptical fiber 2402 being less than or equal to the MFD of the opticalfiber 2916. When the proximal end of the guidewire terminating inconnector portion 2902 is detached, other components can be easilyslipped over the guidewire. The present inventors have determined thatthe desired alignment accuracy of the proximal connection, namely 1micrometer, can be relieved by employing optical pathway devices thatutilize beam spreading techniques such that the optical beam at theconnection interface is significantly larger than the core size utilizedin the standard and reduced cladding fibers, as shown and describedbelow with respect to FIG. 29B.

FIG. 29B shows another example of a proximal region of a guidewireassembly 2900, such as one of the various guidewire assemblies describedherein, terminating at a proximal end connector 2920. Many of thecomponents of FIG. 29B are similar to those shown and described abovewith respect to FIG. 29A and, for purposes of conciseness, will not bedescribed again. It should be noted that the proximal ferrule 2922 ofFIG. 29B defines a conical region, shown at 2924, in contrast to theproximal ferrule 2910 of FIG. 29A.

As indicated above, the guidewire assembly 2900 of FIG. 29B can utilizebeam spreading techniques. Typical beam spreading devices include, butare not limited to lenses, gradient-index (GRIN) lenses, ball lenses andthe like. These devices may be utilized as illustrated in FIG. 29B. Forexample, a first fiber lens 2926, e.g., a GRIN lens, can be attached tothe reduced cladding fiber 2402 in the proximal end of the guidewireassembly 2900, and a second fiber lens 2928, e.g., a GRIN lens, may beattached to the distal end of the standard fiber 2916. The utilizationof these types of lenses can greatly reduce the alignment accuracy ofthe interface, can minimize any optical losses and can also reduce theoptical loss effects of micro contaminants that the physician does notremove from the proximal end of the guidewire. In addition, the reliefof the preferred alignment accuracy requirement allows for the use oflower cost components to hold the fibers and lenses.

FIG. 29C shows another example of a ferrule that can be used incombination with the various guidewire assemblies described herein. Thepresent inventors have recognized that it can be advantageous for one orboth ends of the distal ferrule and the proximal ferrule to be stepped.FIG. 29C depicts an example of a ferrule 2930, which can include asmaller diameter 2932 (or step) at the end of the ferrule 2930, e.g.,the distal end of the distal ferrule 2906 of FIG. 29A. The step 2932 canact as a mechanical stop at its interface into the coupling tube, whichcan protect the fiber as it transitions from the guidewire into theferrule. A very short step at the proximal end of the distal ferrule2906 (FIG. 29A) or the distal end of the proximal ferrule 2910 (FIG.29A) can provide for a relief as the two ferrule faces mate togetherwhere any particles remaining after the connector cleaning could residewithout interfering with the contact of the optical surfaces.

FIG. 29D shows another example of a proximal region of a guidewireassembly 2900 terminating at a proximal end connector 2902 and using theferrule 2930 of FIG. 29C. The step 2932 can act as a mechanical stop forthe ferrule 2930 at its interface into the coupling tube 2904.

Using various techniques described above, changes in ambient pressurecan be detected by measuring the wavelength change, e.g., quantifiedchange in phase-shift, by an FBG sensor within a housing, e.g., housing308 of FIG. 3. As described above with respect to FIGS. 4A-4C and FIG.6A, the change in phase-shift can be quantified by locking a laser at aposition on a slope of the transmission notch of the resonant feature,tracking a particular optical power level in the resonant feature, andadjusting the bias current of the laser which, in turn, subtly changesthe wavelength to maintain this “locked” relationship.

These techniques can produce satisfactory results when the opticalinsertion loss is constant. In some example implementations, however,the overall insertion loss of the pressure sensor and/or system canchange during the measurement, e.g., kinking in the optical fiber. Asshown and described below with respect to FIG. 30, a change in theoptical insertion loss can lead to an artificial shift in the trackingwavelength, and thus an offset error in the pressure reading, if theoptical locking level or threshold is not adjusted accordingly.

FIG. 30 depicts a conceptual response diagram illustrating the effect ofan uncorrected locking level on a locking wavelength. In FIG. 30, wherethe x-axis represents wavelength and the y-axis represents the intensityof the reflected light, a transmission notch 3000 is shown within areflection band 3002, and a reduced reflection band 3004, which iscaused by insertion loss. An initial locking level, or opticalthreshold, 3006 is depicted, which corresponds to a wavelength of about1550.85 nm and a reflection intensity of 50%.

If insertion loss is introduced, which results in the reduced reflectionband 3004, then the locking level may move up or down the slope of thereduced reflection band 3004 in order to maintain its locking level,e.g., 50 o, despite the fact that the transmission notch 3004 has notmoved. If the insertion loss increases (optical power decreases), thenthe shift can be to a higher, incorrect locking wavelength because thelocking circuit climbs the slope of the reduced reflection band 3004 tomaintain the set optical level, as shown at 3008. If the insertion lossdecreases (optical power increases)(not depicted in FIG. 30), then theshift can be to a lower, incorrect locking wavelength because thelocking circuit moves down the slope of the reduced reflection band 3004to maintain the set optical power level. Either of these conditions canlead to a significant drift in the apparent pressure level even if therehas been no phase-shift change in the FBG filter.

As described in more detail below, using various techniques of thisdisclosure, the locking level 3006 can be corrected for insertion loss,resulting in a corrected locking level 3010. In accordance with thisdisclosure, a small dither signal can be added to the wavelength of thelaser at, for example, a frequency outside those associated with thepressure sensing. Then, the AC component, which is the change in theoptical signal reflected from the pressure sensor back to the opticaldetector, e.g., optical detector 608 of FIG. 6A, can be extracted fromthe optical signal via an electronic circuit associated with the opticaldetector. The magnitude of the AC component can then be used to make anyadjustments to the locking level to null out any offset errors.

FIG. 31 depicts the conceptual response diagram of FIG. 30 compensatedfor optical insertion loss in an optical pressure sensor using varioustechniques of this disclosure. In FIG. 31, where the x-axis representswavelength and the y-axis represents the intensity of the reflectedlight, a transmission notch 3000 is shown within a reflection band 3002,and a reduced reflection band 3004, which is caused by insertion loss.

Two AC components 3012, 3014 are depicted in FIG. 31, where the ACcomponent 3012 depicts a magnitude of the AC component with no excessloss and where the AC component 3014 depicts a magnitude of the ACcomponent with excess loss. Thus, the magnitude of the AC component canchange with insertion loss.

As indicated above, a small dither signal 3016 can be added to thewavelength of the laser. Then, an AC component can be extracted from theoptical signal via an electronic circuit associated with the opticaldetector. As can be seen in FIG. 31, the amplitude of the AC components3012, 3014 can vary in proportion to the overall signal level as long asthe amount of wavelength dither is held constant. That is, if thewavelength range of the dither 3016 is held constant, the magnitude ofthe AC component can scale directly with the optical insertion loss.

By comparing a current value of the AC component, e.g., AC component3014, to an initial value of the AC component, e.g., AC component 3012,the controller 602 (FIG. 6A) can determine whether the optical insertionloss has increased or decreased. The current value of the AC componentcan be fed back to the optical locking circuit of FIG. 6A, a portion ofwhich is described below with respect to FIG. 33. Then, because the ACcomponent is reduced in proportion to the change in insertion loss, thecontroller 602 of FIG. 6A can adjust the optical locking levelaccordingly to maintain the correct locking wavelength.

In some examples, a frequency and amplitude of the wavelength dither3016 can be selected so as to be compatible with the pressuremeasurements. For example, for the dither frequency, a value can beselected that is higher than the necessary bandwidth for pressuresensing. Assuming, for example, that the pressure bandwidth is between0-25 Hz, then it might be desirable to select a frequency for thewavelength dither at least five times higher than the pressurebandwidth.

FIG. 32 is a flow diagram illustrating an example of a method 3200 forcompensating for optical insertion loss in an optical pressure sensorusing various techniques of this disclosure. The controller 602 of FIG.6A can establish, or determine, an optical locking level with no excessinsertion loss (3202), e.g., initial locking level 3006 of FIG. 31, andestablish, or determine, an initial amplitude of a dither signal (3204),e.g., the AC component 3012 of FIG. 31, by extracting the dither signalfrom the optical signal reflected from the pressure sensor and measuringits amplitude. The controller 602 can measure a new amplitude of thedither signal (3206), e.g., the AC component 3014 and compare the newamplitude to the initial amplitude (3208). If the insertion loss haschanged (“YES” branch of 3210), as determined by the comparison at 3208,then the controller 602 can control the laser drive current control 614of FIG. 6A or the locking set point value 612 of FIG. 6A to adjust thelocking level to a new value (3212), e.g., if the AC component decreasesthen the locking level is reduced by the appropriate amount. If theinsertion loss has not changed (“NO” branch of 3210), as determined bythe comparison at 3208, then the controller 602 can continue to measurethe new amplitude of the dither signal at 3206.

FIG. 33 is a block diagram of an example of a portion of the lasertracking system of FIG. 6A for compensating for optical insertion lossin an optical pressure sensor using various techniques of thisdisclosure, in accordance with this disclosure. An AC dither generator3312 generates a dither signal that is summed together with the lasercontrol current via summer 3314 and passed to the laser current drivecircuit 614. The laser current drive circuit 614 generates a drivecurrent for laser 604 of FIG. 6A.

An optical signal reflected back from the pressure sensor, e.g.,pressure sensor 300 of FIG. 3, is detected by the optical detector 608,amplified by electrical amplifier 3300, and filtered by a low passfilter 3302, e.g., frequencies of about 0-25 Hz, and a high pass filter3304, e.g., frequencies greater than 25 Hz. The low pass filter 3302passes the DC level to a locking comparator 3306 and the high passfilter 3304 passes the high pass filtered signal, or AC component, tothe controller 602, which measures the amplitude of the dither signal(3308), or AC component, and calculates the optical locking level(3310), e.g., if the AC component decreases then the locking level isreduced to the appropriate value. The controller 602 passes thecalculated optical locking level to the locking comparator 3306, whichcompares the DC level and the calculated optical locking level. Thelaser current drive circuit 614 or the locking set point 612 can beadjusted based on the comparison. In this manner, a constant centerwavelength is maintained. The same result can also be achieved byaccounting for the wavelength shift in the form of a softwarecorrection.

In one example implementation, the frequency of the dither 3016 of FIG.31 can be selected in order to design a low-pass filter 3302 that canreduce the residual AC dither component in the electrical path to thelocking circuit controlled by the laser current drive circuit 614. Thismay be desirable in order to prevent the locking circuit from chasingthe locking level at the frequency of the dither. It may be desirablefor the locking circuit to see the average or DC level of the opticallocking level.

There are many ways to filter the optical signal and only one example ispresented in this disclosure. Other filtering techniques or techniquesfor suppressing the AC component could be employed and are consideredwithin the scope of this disclosure.

In order to ensure that the laser is able to respond to the ditherfrequency chosen without any reduction in the actual wavelength shiftdesired, there may be factors to consider in selecting a ditherfrequency. For example, it has been found that the design of the lasersubmount has an effect on the frequency at which the laser can ditherthe laser.

Typical dither frequencies can range from around 100 Hz to 1000 Hzbefore the response starts to diminish. In one example implementation,it may be desirable to select a dither frequency between about 300 Hzand about 1000 Hz.

The dither magnitude can be selected to have an appropriate scale togive a detectable AC component, e.g., around ±10% of the overall DCsignal level. In this example, if the maximum optical power level isassumed to be about 1000 μW and the slope is assumed to be about 50μW/pm, then it may be desirable to shift the wavelength of the laser bythe equivalent of about ±2 pm (±100 ρW). If the laser is assumed to havea wavelength coefficient of about 5 pm/mA, then this would equate to abias current dither of about ±0.4 mA. These numbers are given forpurposes of illustration only and could be adjusted within sensiblelimits.

The numbers given above for the dither parameters are appropriate forlasers that have a standard design. It may be possible to greatlyincrease the dither frequencies without any diminishing of the frequencyshift by using a laser of a specific design suited to this application.For instance, there are laser designs that utilize a tunable section inthe center of the laser chip that can be modulated at a much higherfrequency. Using such a laser, the dither frequency can be increased to10 kHz or higher, which would be beneficial as it can place the ditherfrequency further from the frequencies of the pressure signal thusallowing better separation.

To summarize, with respect to FIGS. 31-33, this disclosure describes,among other things, the following techniques: compensating for changesin optical insertion loss of the pressure sensor that would otherwise beseen as large drifts in the apparent measured pressure; calculating andadjusting an optical locking level to achieve compensation of changes inoptical insertion loss by wavelength dithering of the tracking laser;applying wavelength dither to a tracking laser to generate a signal withamplitude proportional to optical insertion loss; and applying feedbackto an optical locking level to compensate optical insertion loss.

It should be noted that the dither techniques described above can beused in a similar manner to track the insertion loss of an intravascularultrasound (IVUS) imaging device and to make adjustments to the opticallocking levels. It may also be desirable to make dynamic adjustments toa sensitivity correction matrix for the imaging elements in a receivemode. The quality of imaging can be improved when the sensitivity of theelements are balanced in the reconstruction matrix to reduce side-lobelevels.

A first order calibration of the receive sensitivity of the elements canbe made by measuring the AC component from the wavelength dither as thisindicates the slope of the sensing element. The expected receiveultrasound signal is proportional to the ultrasound energy imparted onthe element (this is converted to a change in the optical cavity lengthor phase-shift) multiplied by the slope of the cavity. Therefore, byknowing the slope from the dither, an expected signal sensitivity fromthe element can be calculated.

In the case of IVUS, the relationship of the frequencies is reversed,where the dither frequency is well below the ultrasound frequencies andis filtered out by the ultrasound electrical circuits.

To summarize, with respect to IVUS imaging devices, this disclosuredescribes, among other things, the following techniques: dynamicallyadjusting optical locking levels; dynamically adjusting an elementcalibration matrix to improve image reconstruction; and calibratingreceive sensitivity of elements based on dither slope measurements. Manyof the techniques described in this disclosure are applicable tointravascular imaging devices, such as those described in Bates & VardiU.S. Pat. Nos. 7,245,789, 7,447,388, 7,660,492, 8,059,923, U.S. Pat.Pub. No. US-2012-0108943-A1, and U.S. Provisional Patent Application No.61/783,716, titled “Optical Fiber Ribbon Imaging Guidewire and Methods”to Tasker et al. and filed on Mar. 14, 2013, each of which is herebyincorporated by reference herein in its entirety.

Turning to another aspect, in any optical system with highly coherentlight sources, e.g., a narrow linewidth laser, there is a possibilitythat any unintended reflections, even very weak ones, can form aresonant optical cavity within the device. The cavity can exhibit astrong frequency component that depends on the optical path length ofthe cavity (in this case the length of optical fiber between reflectionpoints). The frequency of the cavity is given by:

${\Delta \; v} = \frac{c}{2\; L}$

where Δv=frequency separation of maxima (Hz), C=speed of light, andL=optical path length (Length×refractive index). The longer the cavity,the more closely spaced the ripples in the frequency and wavelengthdomains.

A large amount of optical energy can be circulated within the pressuresensing device and, under certain conditions, can form undesirableoptical resonances with other elements of the system. The undesirableresonances can be formed between any two points of optical reflection.For instance, the undesirable resonances can be formed between the FBGsand a system connector, or the FBGs and a pressure wire connector. Inaccordance with this disclosure and as described in more detail belowwith respect to FIGS. 34-37, these undesirable resonances can beaveraged out using dither techniques, thereby reducing their overalleffect on the pressure measurements.

FIG. 34 depicts a conceptual response diagram illustrating undesirableoptical resonances caused by additional reflection in an optical system.In FIG. 34, where the x-axis represents wavelength and the y-axisrepresents the intensity of the reflected light, a transmission notch3400 is shown within a reflection band 3402. The undesirable opticalresonances are shown as ripples 3404 overlaid on the fundamentalresponse. In this example the undesirable reflection point is at adistance of about 70 mm from the FBGs.

In an example of a pressure sensing device, there may be an opticalconnector to the system about two meters from the FBG filters that is apossible source of reflections. The calculated expected wavelength ofthe ripple caused by a reflection at two meters is approximately 0.4 pm(at 1550 nm). There is a possibility that the locking system can becomeconfused by these ripples 3404 and hop between them, which appears as asudden jump in the apparent pressure reading, e.g., 10 mm/Hg, shown anddescribed below with respect to FIG. 35. In the context of pressuresensing, such a jump is unwanted and likely unacceptable due to the needfor accurate pressure measurements.

FIG. 35 depicts the conceptual response diagram of FIG. 34 furtherillustrating undesirable locking circuit wavelength hopping. FIG. 35shows a calculated response for a weak reflection at 70 mm (anon-limiting example for purposes of illustration only) and how thelocking circuit can become confused and shift to a different wavelength.More particularly, the locking circuit can become confused because theoptical locking level 3504 can intersect both the fundamental response3402 (at point 3506) and a ripple 3404 (at point 3508), resulting in twopossible optical locking wavelengths. As a result of the ripple 3404,the desired optical locking wavelength at 3500 can jump to a higheroptical locking wavelength 3502. Assuming that the sensor has apressure-to-wavelength coefficient of around 1 pm for 25 mm/Hg and thatthe 2 m cavity has a ripple period of 0.4 pm, then the apparent shift isapproximately 10 mm/Hg, which is highly undesirable.

In accordance with this disclosure and as described in more detail belowwith respect to FIG. 36, the optical dither techniques described abovecan be used to average through these ripples 3404 and to reduce oreliminate their effects on determining an optical locking wavelength.

FIG. 36 depicts the conceptual response diagram of FIG. 35 compensatedfor optical cavity noise using various techniques of this disclosure. Inaccordance with this disclosure, optical wavelength dither (describedabove) can be used to sweep or average through a number of the rippleperiods. Examples of lower and upper bounds of the dither opticalwavelength are depicted at 3600, 3602, respectively. In the exampleshown in FIG. 36, within the lower and upper wavelength bounds 3600,3602 are four ripples 3404 that can be averaged. Less or more ripplescan be averaged.

When the laser wavelength is dithered, e.g., at a frequency at leastfive times the bandwidth of the pressure signal, the high frequency ACcomponent can be extracted from the optical signal by filtering, similarto what was described above with respect to the insertion losscompensation techniques and as depicted in FIG. 33. If the pressuresignal has a bandwidth of about 0-25 Hz, then the dither frequency is atleast 125 Hz, for example. In other examples, the dither frequency isabout 300-400 Hz.

Once the high frequency AC component is extracted, then the controller602 of FIG. 6 can average the AC component over the region of interest,e.g., over four ripples 3404 as in FIG. 36. The dithering occurs at afaster rate than the rate at which the ripples 3404 move side to sideduring the measurement. As a result, the controller 602 can averagethrough the ripples 3404, thereby removing the optical cavity noise. Thecontroller 602 can then determine an optical locking level andwavelength without becoming confused and jumping to an incorrect opticallocking wavelength.

The amplitude and frequency requirements of the dither wavelength can bemade to complement the insertion loss compensation (described above),e.g., a frequency of about 300-400 Hz. The amplitude of the wavelengthdither can be calculated based on the wavelength separation of theundesirable ripples. In one example, it may be desirable to dither by awavelength amount that would encompass a sufficient number of ripples togive satisfactory averaging. If the ripples are more closely spaced,then the controller 602 can control generation of a relatively smalleramount of dither than if the ripples were more widely spaced to achievethe same amount of averaging. Take, for example, a two meter longdistance between the reflection points, the calculated wavelength of theripple caused by a reflection at two meters is approximately 0.4 pm (at1550 nm), then it may be desirable to dither the wavelength of the laserby 5 ripple periods to give satisfactory averaging. The wavelength ofthe laser can be dithered by a total of 2 pm (0.4 pm×5 ripples). Thiscorresponds to a dither in the laser current of around 0.4 mA, where atypical laser is 5 pm/mA.

In one example implementation, the same dither frequency and electricalfiltering used for the insertion loss compensation techniques describedabove can be used to compensate for the optical cavity noise to allowthe usual detection of the pressure readings in the 0-25 Hz bandwidth.In some example implementations, the low frequencies, e.g., 0-25 Hz,that correspond to the pressure signals can be used to control thelocking circuit in order to reduce the confusion presented by individualripples. In one example, the electrical filter circuits can be used topresent the average optical detector value to the locking circuits, thusreducing the discrete step nature of the individual ripples.

FIG. 37 depicts a flow diagram illustrating an example of a method 3700for compensating for optical cavity noise in an optical pressure sensorusing various techniques of this disclosure. In FIG. 37, the controller602 of FIG. 6 can control the laser 604 to generate a dither signal at afrequency outside of the range associated with a pressure signal (3702).For example, for a pressure signal having a bandwidth of about 0-25 Hz,the dither frequency can be at least 125 Hz. In one specific example,the dither frequency can be about 300-400 Hz. Next, the optical detector608 of FIG. 6A can receive the reflected optical signal from thepressure sensor (3704). A low pass filter, e.g., filter 3302 of FIG. 33,can remove or suppress the AC component at the dither signal frequency(3706). Then, the controller 602 can determine a low frequency value,e.g., the average locking level in the low frequency band (0-25 Hz),over the specified region of interest of the signal, e.g., over fourripples (3708). Finally, the controller 602 can determine a noisecompensated optical locking wavelength based on the determined averagelow frequency value (3710).

FIG. 38 depicts another example of a portion of a pressure sensorassembly 3800. The pressure sensor assembly 3800 is similar in somerespects to the concentric pressure sensor assembly 2400 depicted inFIG. 24. The pressure sensor assembly 3800 can include or be coupled toan optical fiber 3802, such as a reduced-diameter longitudinallyextending central optical fiber 3802. The pressure sensor assembly 3800can be located at or near a distal region of the optical fiber 3802.

The pressure sensor assembly 3800 can include a housing that includes aproximal housing portion 3806 and a distal housing portion 3804separated by a window portion 3808. As described above with respect toFIG. 24, the proximal portion 3806 and the distal portion 3804 can bemade from a hard, solid, or inelastic (e.g., fused silica) tubular orother housing. The window portion 3808 can be a soft, flexible, elastic,or compliant gasket located between the distal and proximal portions3804, 3806 (e.g., silicone or polyurethane elastomer materials, pressuresensitive adhesive materials, or hot melt adhesive materials).

The optical fiber 3802 enters a proximal end 3810 of the proximalhousing portion 3806 and can be securely captured, anchored, or affixedto the proximal housing portion 3806 via a tubular or other attachment(e.g., hardened epoxy or other adhesive) region 3812. Similarly, theoptical fiber exits a distal end 3814 of the distal housing portion 3804and can be securely captured, anchored, or affixed to the distal housingportion 3804 via a tubular or other attachment (e.g., hardened epoxy orother adhesive) region 3816.

The pressure sensor assembly 3800 of FIG. 38 can further include asensing region that can include two FBGs, namely FBG 1 and FBG 2. Asseen in FIG. 38, and in contrast to the concentric pressure sensorassembly 2400 of FIG. 24, an FBG, namely FBG 2, can extend distallybeyond the distal end of the pressure sensor assembly 3800. By extendingbeyond the distal end of the pressure sensor assembly, the FBG 2 can bein direct contact with a bodily fluid, for example. In such an exampleconfiguration, any effect that securing materials, e.g., epoxies, mayhave on the FBG 2 can be eliminated. In addition, by extending the FBG 2beyond the distal end of the pressure sensor assembly 3800 instead ofcontaining the FBG 2 within the housing, the length of the housing ofthe pressure sensor assembly 3800 can be reduced. In some exampleconfigurations, FBG 1 can be used to measure both pressure andtemperature while FBG 2 can be configured to measure ambienttemperature, e.g., of the bodily fluid, thereby providing an example ofa temperature compensated pressure sensor. In one example configuration,it may be desirable to include a non-reflective termination as close tothe distal end of the FBG 2 as possible. Without such a termination, areflection can modulate the optical signal returning from the pressuresensor, which can affect the accuracy of the measurements.

FIGS. 39-41 depict examples of portions of various pressure sensorassemblies. Each of the various pressure sensor assemblies depicted inFIGS. 39-41 include an FBG that extends distally beyond the distal endof each respective pressure sensor assemblies.

The example of a pressure sensor assembly depicted in FIG. 39 is similarto the pressure sensor assembly 3800 described above with respect toFIG. 38 and, as such, will not be described in detail again for purposesof conciseness. In some example configurations, each of FBG 1 and FBG 2can include a phase shift, e.g., 180 degrees, in the center of the FBG.The phase shift can create a notch in the response, which can be trackedusing a tracking circuit as described above.

FIG. 40 depicts an example of a pressure sensor assembly 4000 that caninclude four FBGs, namely FBGs 1-4. The pressure sensor assembly 4000can include or be coupled to an optical fiber 4002, such as areduced-diameter longitudinally extending central optical fiber 4002.The pressure sensor assembly 4000 can be located at or near a distalregion of the optical fiber 4002.

The pressure sensor assembly 4000 can include a housing that includes adistal housing portion 4004 and a proximal housing portion 4006separated by a window portion 4008. As described above with respect toFIG. 24, the distal portion 4004 and the proximal portion 4006 can bemade from a hard, solid, or inelastic (e.g., fused silica) tubular orother housing. The window portion 4008 can be a soft, flexible, elastic,or compliant gasket located between the distal and proximal housingportions 4004, 4006.

The optical fiber 4002 enters a proximal end 4010 of the proximalhousing portion 4006 and can be securely captured, anchored, or affixedto the proximal housing portion 4006 via a tubular or other attachment(e.g., hardened epoxy or other adhesive) region 4012. Similarly, theoptical fiber 4002 exits a distal end 4014 of the distal housing portion4004 and can be securely captured, anchored, or affixed to the distalhousing portion 4004 via a tubular or other attachment (e.g., hardenedepoxy or other adhesive) region 4016.

The pressure sensor assembly 4000 of FIG. 40 further includes a sensingregion that can include four FBGs, namely FBGs 1-4. As seen in FIG. 40,an FBG, namely FBG 3, extends distally beyond the distal end of thepressure sensor assembly 4000. By extending beyond the distal end of thepressure sensor assembly, the FBG 3 can be in direct contact with abodily fluid, for example. In such an example configuration, any effectthat securing materials, e.g., epoxies, may have on the FBG 3 can beeliminated. In addition, by extending the FBG 3 beyond the distal end ofthe pressure sensor assembly 4000 instead of containing the FBG 3 withinthe housing, the length of the housing of the pressure sensor assembly4000 can be reduced.

In some example configurations, from left to right, FBG 4 can be used tomeasure pressure, FBG 1 can be used to measure temperature, FBG 2 can beused to measure pressure, and FBG 3 can be configured to measure ambienttemperature, e.g., of the bodily fluid, thereby providing an example ofa temperature compensated FBG interferometer in optical communicationwith the optical fiber 4002. Increasing the distance between the twotemperature gratings, namely FBG 1 and FBG 3, increases the finesse,which can increase the sensitivity of the sensor, e.g., a steeper slopein the reflection band, and improve the quality factor.

FIG. 41 depicts an example of a pressure sensor assembly 4100 that caninclude three FBGs, namely FBGs 1-3. The pressure sensor assembly 4100can include or be coupled to an optical fiber 4102, such as areduced-diameter longitudinally extending central optical fiber 4102.The pressure sensor assembly 4000 can be located at or near a distalregion of the optical fiber 4102.

The pressure sensor assembly 4100 can include a housing that includes adistal housing portion 4104 and a proximal housing portion 4106separated by a window portion 4108. As described above with respect toFIG. 24, the distal housing portion 4104 and the proximal housingportion 4106 can be made from a hard, solid, or inelastic (e.g., fusedsilica) tubular or other housing. The window portion 4108 can be a soft,flexible, elastic, or compliant gasket located between the distal andproximal housing portions 4104, 4106.

The optical fiber 4102 enters a proximal end 4110 of the second housingportion 4106 and can be securely captured, anchored, or affixed to thesecond housing portion 4106 via a tubular or other attachment (e.g.,hardened epoxy or other adhesive) region 4112. Similarly, the opticalfiber exits a distal end 4114 of the first housing portion 4104 and canbe securely captured, anchored, or affixed to the first housing portion4104 via a tubular or other attachment (e.g., hardened epoxy or otheradhesive) region 4116.

The pressure sensor assembly 4100 of FIG. 41 further includes a sensingregion that can include three FBGs, namely FBGs 1-3. As seen in FIG. 41,an FBG, namely FBG 3, extends distally beyond the distal end of thepressure sensor assembly 4100. By extending beyond the distal end of thepressure sensor assembly, the FBG 3 can be in direct contact with abodily fluid, for example. In such an example configuration, any effectthat materials, e.g., epoxies, may have on the FBG 3 can be eliminated.In addition, by extending the FBG 3 beyond the distal end of thepressure sensor assembly 4100 instead of containing the FBG 3 within thehousing, the length of the housing of the pressure sensor assembly 4100can be reduced.

In some example configurations, one of the three FBGs can have aresponse that is larger than the response of the other two FBGs. Forexample, one of the FBGs, e.g., FBG 2, can have a response with abouttwice the bandwidth as either FBG 1 or FBG 3. FBG 1 and FBG 3 can eachhave a narrowband response that resonates with a different portion ofthe grating of FBG 2.

In one example, FBG 1 can be used to measure pressure, e.g., narrowbandresponse, FBG 3 can be used to measure temperature, e.g., narrowbandresponse, and FBG 2 can be used to measure pressure, e.g., broadbandresponse. As described above, in order to generate a pressure signalthat is ambient temperature compensated, the signal generated by FBG 3can be used as a reference to null a shift in temperature. A controllercircuit can be configured to control subtraction of the temperaturereference signal (from FBG 3) from the pressure signals (from FBGs 1 and2), such as to generate a temperature compensated pressure signal. Anexample of a temperature compensation technique was described above withrespect to FIG. 5.

FIG. 42 depicts another example of a guidewire in combination with anoptical fiber pressure sensor assembly. In FIG. 42, an optical pressuresensor assembly 4200, e.g., assemblies 3900, 4000, and 4100 of FIGS.39-41, can be delivered to a desired site using a guidewire, showngenerally at 4202. The guidewire 4202 can include a core wire 4204, aproximal coil 4206, and a distal coil 4208. The proximal coil 4206 andthe distal coil 4208 can be joined together via a mechanical joint 4210,e.g., solder or adhesive.

The optical pressure sensor assembly 4200 can be mounted to the corewire 4204 via a mounting unit 4214. In turn, the mounting unit 4214 canthen be attached to a coil, e.g., proximal coil 4206.

The guidewire 4202 can further include one or more disk spacers 4212A,4212B (referred to collectively in this disclosure as disk spacers4212). The disk spacers 4212 can define a hole through which the opticalfiber 4216 can extend. The disk spacers 4212 can be included to preventthe optical fiber 4216 from contacting other components of the guidewire4202, e.g., coils 4206, 4208.

FIGS. 43A-43C depict another example of a guidewire in combination withan optical fiber pressure sensor. In FIG. 43A, an optical pressuresensor assembly 4300, e.g., assemblies 3900, 4000, and 4100 of FIGS.39-41, can be delivered to a desired site using a guidewire, showngenerally at 4302. The guidewire 4302 can include a core wire 4304, aproximal coil 4306, and a distal coil 4308. The proximal coil 4306 andthe distal coil 4308 can be joined together via a mechanical joint 4310,e.g., solder or adhesive.

The guidewire 4302 can further include a cradle 4312 to providestiffness around the sensor assembly 4300. The cradle 4312, e.g.,U-shaped, is shown in more detail in FIG. 43B. As seen in FIG. 43A, theoptical pressure sensor assembly 4300 can fit within the cradle 4312.The optical fiber 4314 can extend into and out of the cradle 4312, andthe cradle 4312 can fit inside the coils 4306, 4308. The pressure sensorassembly 4300 can be mounted to the core wire 4304 via a mountingmaterial 4316, e.g., an epoxy, which can extend through the cradle 4312.

FIG. 43C depicts a cross-sectional view of the guidewire assembly shownin FIG. 43A. As seen in FIG. 43C, a portion of the diameter of the corewire 4304 can be reduced over a length of the cradle 4312 to providesufficient room for mounting the pressure sensor assembly 4300.

FIGS. 44A-44C depict another example of a guidewire in combination withan optical fiber pressure sensor. In FIG. 44A, an optical pressuresensor assembly 4400, e.g., assemblies 3900, 4000, and 4100 of FIGS.39-41, can be delivered to a desired site using a guidewire, showngenerally at 4402. The guidewire 4402 can include a core wire 4404, aproximal coil 4406, and a distal coil 4408.

The guidewire 4402 can further include a tube assembly 4412 to providestiffness around the sensor assembly 4400. The tube assembly 4412 isshown in more detail in FIG. 44B. The tube assembly includes a proximalend portion 4414 and a distal end portion 4416 that extend from theproximal and distal ends 4418, 4420, respectively, of a main body 4422of the tube assembly 4412. A portion of the circumference of the mainbody 4422 of the main body 4422 can be removed to allow pressure signalsto reach the pressure sensor assembly 4400.

As seen in FIG. 44A, the optical pressure sensor assembly 4400 can fitwithin the tube assembly 4412. The optical fiber 4424 can extend intoand out of the tube assembly 4412. In contrast to the guidewire designin FIGS. 43A-43C, the tube assembly 4412 does not fit within the coils4406, 4408. Instead, the coils 4406, 4408 can be affixed, respectively,to the proximal end portion 4414 and the distal end portion 4416 thatextend from the proximal and distal ends 4418, 4420 respectively, of thetube assembly 4412. The pressure sensor assembly 4400 can be mounted tothe core wire 4404 via a mounting material 4426, e.g., an epoxy, whichcan extend through the tube assembly 4412.

FIG. 44C depicts a cross-sectional view of the guidewire assembly shownin FIG. 44A. As seen in FIG. 44C, a portion of the diameter of the corewire 4404 can be reduced over a length of the tube assembly 4412 toprovide sufficient room for mounting the pressure sensor assembly 4400.

FIGS. 45A-45B depict an example of a core wire, shown generally at 4500,that can be used in combination with an optical fiber pressure sensor.During manufacture, the diameter of the core wire 4500 can be variedover specified lengths in order to form a desired shape. For example, asseen in FIG. 45A, the core wire 4500 can be manufactured to include aportion 4502 with a diameter that is larger than the remaining proximalor distal portions 4504, 4506, respectively, of the core wire 4500. Thecore wire 4500 can be manufactured to include one or more taperedportions 4508A-4508C that taper the portion 4502 from its largerdiameter to the smaller diameter of the proximal and distal portions4504, 4506.

After the core wire 4500 has been manufactured to the desireddimensions, a cradle can be formed, for example, in enlarged portion4502, e.g., using a coining process, precision machining, micromachiningmicro EDM, or other processes, in the portion(s) with a larger diameter,as shown generally at 4510 in FIG. 45B. The cradle 4510 formed in thecore wire 4500 can be used to provide a housing for a pressure sensorassembly, e.g., assemblies 3900, 4000, and 4100 of FIGS. 39-41, as shownin FIG. 46A-B.

The cradle 4510 can have varying inside dimensions to provide theability to secure the sensor in varying ways. For example, in someembodiments, it may be advantageous to mount the sensor at its proximalportion only and to allow the rest of the sensor to be cantilevered inthe cavity such that it cannot be touched during normal use of theguidewire. This arrangement can minimize the likelihood of guidewirebending producing erroneous or artificial pressure readings. In otherembodiments, the cradle 4510 can have a shape that is rectangular ornon-rectangular.

By way of example, the cradle 4510 as shown can have a shape thatenables the mounting of a cylindrical shaped sensor without removingmore material than necessary, which helps maintain the relativestiffness of the core in the region of the sensor. The cradle 4510, forexample, may have a complex shape or it may have a semi-cylindricalshape. By way of example, the cradle of FIG. 45B has a size and shapethat by itself does not protect the sensor. The sensor placed therein,as shown in FIG. 46, can be mounted such that the upper extremity of thecylindrical surface is higher than the side walls of the cradle 4510.

Such a cradle and core design can be advantageous because a singlestructure can function both as the core wire 4500 and as the housing ofa pressure sensor assembly, which can improve its strength. In addition,the design of FIG. 45B can be advantageous because the core wire 4500 iscoaxial with the guidewire, as shown in FIG. 46A, which can enhance theperformance of the guidewire. For example, the guidewire can improve thesteering of the guidewire and allow the guidewire to perform morepredictably, e.g., without whip or latency, which can be important whileassessing a lesion.

FIG. 46A depicts an example of a guidewire in combination with anoptical fiber pressure sensor and the core wire of FIG. 45B. In FIG.46A, an optical pressure sensor assembly 4600, e.g., assemblies 3900,4000, and 4100 of FIGS. 39-41, can be delivered to a desired site usinga guidewire, shown generally at 4602. The guidewire 4602 can include acore wire 4604, e.g., the core wire 4500 of FIG. 45B, a proximal coil4606, and a distal coil 4608. As described above, the core wire 4604 canbe formed to include a cradle 4610, e.g., the cradle 4510 of FIG. 45B,which can hold the pressure sensor assembly 4600. An optical fiber 4612can extend along the core wire 4604. As seen in FIG. 46A, the core wire4604 is coaxial with the guidewire 4602, which can enhance theperformance of the guidewire.

Optical pressure sensor assembly 4600 can be seen mounted on the cradle4610 in a cantilevered way. The degree of cantilever can be varied byvarying the length of the mount which attaches to the proximal body of4600. The rest of the cavity can be formed such that there is a gaparound the distal body and the sensitive distal end of 4600. The corewire 4604, in the section defining the sensor mount, can be varied insize and shape. For example, the outside diameter of the cradle 4610 canhave a constant diameter section and one or more tapered sections. Thecoil 4606 can, for example, be attached to the cradle 4610 at theconstant diameter section and not at the tapered section such that theeffect is to minimize the relatively stiff length of the construction inthis area. This can be helpful in providing enhancements to themechanical performance of the guidewire.

In another example, as mentioned in regard to FIG. 45B, the cradle canbe sized and shaped such that sensor 4600 is not fully protected by thecradle. Such a configuration is shown in the cross-sectional view ofFIG. 46B. In this example, coil 4606 can form an integral part of theprotection means for the sensor 4600. The cradle 4610, in combinationwith the coil 4606, can form a housing that surrounds the sensor 4600and completes the protection mechanism. The coil 4606 and the cradledenlarged portion of the core wire can be joined together to form a solidprotection means. The joining process could be a suitable adhesive,solder or braze.

The smaller distal coil diameter (which can result from the largerdiameter distal coil wire), shown in the example of a guidewire incombination with an optical fiber pressure sensor of FIG. 46A-B can beaccommodated by reducing the diameter of the ground feature at itsdistal end. Alternatively, the distal coil inside diameter can beincreased by forming the distal coil with a smaller diameter wire or aflattened wire thereby allowing both the proximal and distal coils tofit over the sensor protecting feature on the wire. It may also beadvantageous to both reduce the distal diameter of the wire groundfeature only slightly and increase the distal coil ID only slightly tofit the distal coil over the sensor protective feature.

It can also be advantageous to include a small through feature orchannel in the distal end of the sensor housing, e.g., sensor housing5014, to facilitate equalizing pressure within the pressure sensorhousing cavity and the environment in which the distal end of the wireis positioned. In addition, a slight spreading of the coil loops overthe location of the pressure communication channel can be included. Thechannel can be a straight through hole, but a wide variety of channelsas well as starting and ending locations of the channel from the outsideof the core wire through to the inside of the pressure sensor housingcavity can be utilized. It can be advantageous to have more than onechannel for a variety of reasons, such as, for instance that eachindividual channel could be smaller, or placing them in the mostfavorable locations, etc.

Despite being exceptionally low-loss signal carriers, optical fibers canstill attenuate optical signals, especially if the optical fiber isdeformed in certain undesirable manners. Optical signals can beattenuated by, for example, macrobends and microbends in the opticalfiber. Macrobending attenuation can occur when there are relativelylarge bends in the optical fiber significantly exceeding the diameter ofthe optical fiber. As the bend radius decreases, increasing amounts oflight can leak out of the fiber due to lessening optical confinement.Microbending attenuation can occur when there are very small, e.g.,microscopic, deformations of the optical fiber. These deformations canbe caused, for example, by external forces applied to the optical fiber.For example, imperfections of the optical fiber coating or imperfectionsof a surface in contact with the optical fiber can impart forces on theoptical fiber, which can create microbend induced variability in theoptical losses.

The present inventors have determined that microbending losses cancontribute to variability of the optical signal level as the guidewireis flexed, which can reduce the accuracy and stability of a measuredpressure wave. The significance of a flow reducing lesion in a coronaryartery can be determined by accurately measuring the Fractional FlowReserve (FFR) under hyperemic conditions. Since the FFR index can beused to determine the significance of a flow reducing lesion in anartery, with a typical go/no go value of 0.8, for example, smallinaccuracies in pressure readings can lead to incorrect decisions abouttreatment. It is desirable that a pressure sensing guidewire be able toaccurately measure blood pressure. Minimization, or elimination, of thevariable losses can improve signal quality and thus the accuracy of thedevice.

The present inventors have determined that microbending losses can bereduced, for example, by utilizing a wavelength of light which, giventhe size constraints of the guidewire and therefore the size constraintsof the cladding and coating of the optical fiber, has more robustoptical confinement. For example, a wavelength of 1310 nanometers can beused instead of 1550 nanometers. For a given optical fiber, if a lowerwavelength of light is used, typically the diameter of the optical modefield can be reduced. In a standard size optical fiber this might not beof significant consequence but with the ultra reduced diameter of thefiber in this application it significantly reduces the amount of opticalenergy that interacts with the outer circumference of the fiber wherethere is an interface between the optical fiber and the fiber coating.With a reduction in energy at the outer circumference, the optical fiberwill have a lower optical insertion loss.

A standard optical coating applied to optical fibers often has arefractive index that is higher than the refractive of the fibercladding, which can strip any stray light from the cladding so that itcannot interfere with the light in the core of the fiber. This can beundesirable if the mode field of the light in the core is too close tothe interface of the cladding and the optical coating due to the verysmall size of the fiber used in this application. If the insertion lossis too great then it is possible to reduce this by using an opticalcoating that has a refractive index lower than the refractive index ofthe cladding, which can help confine the optical mode field and reducethe insertion loss. It is also possible to achieve a similar desiredeffect by having a doped outer ring in the fiber cladding. This can beachieved by doping a small portion of the outer diameter of the fiberpreform with an additive such as Fluorine. This is inherently embeddedin the fiber as it is drawn from the preform unlike the coating which asapplied to the fiber after it is drawn from the preform.

It can also be desirable to choose the mechanical properties of theoptical coating such that it does not communicate surface imperfectionsto the optical fiber. This can mean choosing an optical coating whosemechanical modulus is soft enough that imperfections in the surroundingmaterials are dissipated through the volume of the coating rather thanbeing transferred to the fiber.

FIG. 63A is a cross-sectional view depicting an example of an opticalfiber having a single coating, in accordance with this disclosure. FIG.63A depicts an optical fiber 6300 having a fiber core 6302 surrounded bya fiber cladding 6304. The optical fiber 6300 can include a low modulus(soft), single fiber coating 6306 to dissipate any surfaceirregularities volume of the coating rather than being transferred tothe optical fiber core 6302.

However, a very soft fiber coating can be accidently removed from thefiber by mechanical abrasion thereby leaving the fiber unprotected. Toreduce the likelihood of this happening, it can be desirable to add anouter coating that is more resistant to mechanical abrasion.

FIG. 63B is a cross-sectional view depicting an example of an opticalfiber having a dual coating, in accordance with this disclosure. FIG.63B depicts an optical fiber 6308 having a fiber core 6302 surrounded bya fiber cladding 6304. Like in FIG. 63A, the optical fiber 6308 caninclude a low modulus (soft), soft fiber coating 6306 to dissipate anysurface irregularities volume of the coating rather than beingtransferred to the optical fiber core 6302. In addition, the opticalfiber 6308 can include a second coating 6310 surrounding the soft fibercoating 6306. The second coating 6310 can be a hard, durable coatingthat is more resistant than the soft fiber coating 6306 to mechanicalabrasion.

For a given fiber design, the lower wavelength will usually be lesssusceptible to microbends and the resulting attenuation lower due tomore robust optical confinement of the optical mode as long as thewavelength stays above the cutoff wavelength of the fiber, which is thewavelength below which the fiber ceases to be single mode.

There are other ways to lessen the undesirable outcoupling of light byadvanced designs in the fiber. These can include carefully tailoredwaveguide designs referred to in this disclosure as depressed claddingdesigns, which is where an area around the core of the fiber isdeliberately lowered in refractive index by adding a dopant such asfluorine.

FIGS. 64A and 64B are conceptual illustrations of fiber profiles. FIG.64A depicts a standard fiber profile 6400 and FIG. 64B depicts amodified profile 6402 utilizing a depressed cladding. In FIGS. 64A and64B, the x-axis represents the fiber cross-section and the y-axisrepresents the refractive index. In contrast to the generally uniformrefractive index adjacent the core in the standard fiber profile 6400 ofFIG. 64A, the refractive index area around the core of the fiber can bedeliberately lowered, as shown in FIG. 64B, by adding a dopant, e.g.,fluorine. The lowering of the refractive index ring around the core canmake the effective index difference appear to be relatively larger andthus is it more difficult for the light to be coupled out of the core bybending.

Additionally or alternatively, it can be desirable to eliminate anyvariable optical losses as the guidewire is twisted and bent in normaluse within a tortuous body lumen, e.g., coronary artery. Typically, thedistal end of a guidewire is designed with certain flexibility andtorque transmission characteristics that enhance the ability to steerthe guidewire into various branches of the coronary artery tree, forexample, including the ability to cross stenoses of variable severity.When incorporating the optical fiber into typical guidewireconstructions, it can be desirable to ensure that the optical fiber isnot subjected to varying external pressures or pinch points along itslength, particularly along the length that is incorporated in thedistal, most flexible, region of the guidewire. Typically, this involvesplacing this length of optical fiber in between the core wire and theouter coil of the guidewire.

The present inventors have determined that the accuracy and stability ofthe optical pressure sensing guidewire can be improved by adding designelements that help reduce or eliminate the variability in optical lossesalong the length of the optical fiber caused by microbends, as shown anddescribed below with respect to FIGS. 47 and 48. For example, thepresent inventors have found that it is preferable to create “channels”within this region that protect the optical fiber with a designobjective of eliminating forces on the optical fiber that may createmicrobends.

FIG. 47 depicts an example of a guidewire in combination with an opticalfiber pressure sensor assembly that can be used to reduce the effects ofmicrobending, using various techniques of this disclosure. FIG. 47depicts a fiber pressure sensor assembly 4700, such as described abovein numerous example configurations. As described in detail above, thefiber pressure sensor assembly 4700 can include a guidewire 4702 havinga core wire 4704 and a coil 4706 disposed about a distal portion of thecore wire 4704.

An optical fiber 4708 can be wound about the guidewire 4702 and the corewire 4704 underneath the coil 4706. The optical fiber 4708 can be woundaround the core wire 4704 with or without any adhesive to attach the twotogether. As the two components flex in normal use, the relativelysmooth surface of the core wire 4704 does not impart microbends into theoptical fiber 4708. However, with the coil 4706 in place around the twocomponents, the coil 4706 can contact the optical fiber 4708 in normaluse, which can create pinch points or impart microbends into the opticalfiber 4708.

In accordance with this disclosure, the fiber pressure sensor 4700 caninclude stand-offs or channels that can protect the optical fiber 4708from being touched by the coil 4706, and thus prevent microbends. Forexample, one or more filament members 4710A, 4710B (collectivelyreferred to in this disclosure as “filament members 4710”) can behelically wound around the core wire 4704 between the windings of theoptical fiber 4708. The filament members 4710 may be constructed offlexible materials, e.g., metallic or polymeric, that can prevent thecoil 4706 from physically contacting the optical fiber 4708 withoutsubstantially changing the mechanical performance characteristics of theguidewire 4702.

As seen in FIG. 47, the paired filament members 4710A, 4710B can definea channel 4712 within which the optical fiber 4708 can be positioned. Byusing filament members 4710 that have a dimension, e.g., an outerdiameter, greater than the outer diameter of the optical fiber 4708, thefilament members 4710 can prevent the coil 4706 from contacting theoptical fiber 4708.

FIG. 48 depicts another example of a guidewire in combination with anoptical fiber pressure sensor assembly that can be used to reduce theeffects of microbending, using various techniques of this disclosure.FIG. 48 depicts a fiber pressure sensor assembly 4800, such as describedabove in numerous example configurations. As described in detail above,the fiber pressure sensor assembly 4800 can include a guidewire 4802having a core wire 4804 and a coil 4806 disposed about a distal portionof the core wire 4804.

Instead of the filament members described above and depicted in FIG. 47,the fiber pressure sensor assembly 4800 of FIG. 48 can include a ribbonmember 4810, e.g., tape-like member, that can be wrapped around the corewire 4804, and define a channel 4812 within which the optical fiber 4808can be positioned. The ribbon member 4810 can have a dimension, e.g.,thickness, that is greater than the outer diameter of the optical fiber4808, thereby preventing the coil 4806 from contacting the optical fiber4808. In some example configurations, the ribbon member 4810 can be ofuniform thickness. In other example configurations, the ribbon member4810 can be of varying thickness, which can accommodate tapers in thecore wire 4804. In some examples, the ribbon member 4810 can besubstantially flat.

The ribbon member 4810 can create stand-offs or channels that canprotect the optical fiber 4808 from being touched by the coil 4806, andthus prevent microbends. The ribbon member 4810 may be of flexiblematerials, e.g., metallic or polymeric, that can prevent the coil 4806from physically contacting the optical fiber 4808 without substantiallychanging the mechanical performance characteristics of the guidewire4802. By using a ribbon member 4810 that has a thickness greater thanthe outer diameter of the optical fiber 4808, the ribbon member 4810 canprevent the coil 4806 from contacting the optical fiber 4808.Alternatively, the ribbon member design can be accomplished by castingin place a suitable layer of, for example, flexible polymer material.Once the layer of polymer material is in place, the channels for theoptical fiber can be created by selective removal of the polymermaterial using scribing techniques or laser ablation. The polymermaterial may be of uniform thickness, or may be of variable thickness,or may be of uniform or variable outer diameter.

The filament members 4710 and the ribbon member 4810 can be referred tocollectively as stand-off members. As described above and seen in FIGS.47 and 48, these stand-off members are configured to prevent the coilfrom contacting the optical fiber positioned therebetween.

In some example configurations, the stand-offs need not be created by aseparate structure, e.g., the filament members 4710 and the ribbonmember 4810 of FIGS. 47 and 48. Instead, the stand-offs can be formed asa feature of the core wire 4804 during its fabrication (not depicted),e.g., integral to the core wire. For example, during fabrication of thecore wire 4804, protrusions can be created that extend outwardly from anouter surface of the core wire 4804. These protrusions can serve asstand-offs to create channels within which an optical fiber can bepositioned.

Alternatively or additionally, in one example configuration, a groove(not depicted) can be created in the core wire 4804 within which theoptical fiber 4808 can be positioned. The optical fiber 4808 canpositioned within the groove such that it is below the outer surface ofthe core wire, thereby preventing the coil from contacting the opticalfiber.

It should be noted that in any of the above construction examples theoptical fiber may be loosely coiled around the core wire, or it may beadhesively bonded to the core wire. In this latter case, the presentinventors have determined that variability in the thickness of anadhesive so used can adversely affect the optical signal as microbendscan be created at variances or discontinuities of the adhesive.

The present inventors have determined that a uniformly applied adhesive,such as a coating on the core wire, or a jacket on the optical fiber,performs much more favorably. In some examples, the optical fiber can bedisposed within a groove and an adhesive can be uniformly applied overthe top of the optical fiber.

In other examples, the optical fiber can be pre-coated with an adhesive,e.g., a hot melt adhesive, with a uniform thickness. Then the coatedoptical fiber can be positioned within a groove of the core wire andheated such that the adhesive flows. It should be noted that thestand-off techniques described above with respect to FIGS. 47 and 48 arenot limited to sensing guidewires such as those described throughoutthis disclosure. Rather, it may be desirable to incorporate thesestand-off techniques with non-sensing guidewires to keep the core wireand coil concentric and improve the torque to the distal tip of theguidewire.

FIG. 49 depicts another example of a guidewire in combination with anoptical fiber pressure sensor assembly that can be used to implementvarious techniques of this disclosure. FIG. 49 depicts a fiber pressuresensor assembly 4900, such as described above in numerous exampleconfigurations. As described in detail above, the fiber pressure sensorassembly 4900 can include a guidewire 4902 having a core wire 4904.

In contrast to the designs above that include a proximal coil, the fiberpressure sensor assembly 4900 can include a flexible slotted tube 4906having one or more slots 4907 along its length. In some examples, theslots 4907 can be generally perpendicular to a longitudinal axis of theslotted tube 4906. As in other designs described above, the fiberpressure sensor assembly 4900 can include a distal coil 4908.Proximally, the slotted tube 4906 can be attached to the core wire 4904incorporating the groove 4910 for the optical fiber 4912, as shown,utilizing adhesive, solder, welding, or other suitable techniques.Distally, the slotted tube 4906 may be attached to the sensor housing4914 containing sensor 4915 using similar techniques. Alternatively, theslotted tube 4906 can be substituted by a spiral cut tube that impartsflexibility and strength. The spiral cut tube or the slotted tube, insome configurations, can also include a metallic polymer inner tube orliner tube.

FIG. 50 depicts another example of a guidewire in combination with anoptical fiber pressure sensor assembly that can be used to implementvarious techniques of this disclosure. FIG. 50 depicts a fiber pressuresensor assembly 5000, such as described above in numerous exampleconfigurations. As described in detail above, the fiber pressure sensorassembly 5000 can include a guidewire 5002 having a core wire 5004.

Like the example configuration depicted in FIG. 49, the fiber pressuresensor assembly 5000 of FIG. 50 includes a proximal slotted tube 5006having a plurality of slots 5007 along its length. Proximally, theslotted tube 5006 can be attached to the core wire 5004 incorporatingthe groove 5010 for the optical fiber 5012, as shown, utilizingadhesive, solder, welding, or other suitable techniques. Distally, theslotted tube 5006 may be attached to the sensor housing 5014 containingsensor 5015 using similar techniques.

In the example configuration shown in FIG. 50, the spacing of the slots5007 may be varied along a length of the slotted tube 5006. As seen inFIG. 50, the slots 5007 can be placed closer to one another at one end,e.g., the distal end 5016 of the slotted tube 5006, then the other end.

In addition, the core wire 5004 disposed within the slotted tube 5006can be discontinuous along a length of the slotted tube 5006. That is, agap 5018 can exist between a distal portion 5020 of the core wire 5004and the sensor housing 5014 such that a portion of the optical fiber5012 in the gap 5018 is not affixed or otherwise in contact with thecore wire 5004. The variation in flexibility provided by the grooved,continuous profile of the core wire 4904 of FIG. 49 can instead beachieved by varying the pattern and frequency of the slots 5007 in theslotted tube 5006, for example, as shown in FIG. 50. The optical fiber5012 can extend from the distal end 5020 of the grooved, solid coreguidewire 5002 through the slotted tube 5006 to the separate distalsensor housing 5014.

FIG. 51 depicts another example of a guidewire in combination with anoptical fiber pressure sensor assembly that can be used to implementvarious techniques of this disclosure. FIG. 51 depicts a fiber pressuresensor assembly 5100, such as described above in numerous exampleconfigurations. As described in detail above, the fiber pressure sensorassembly 5100 can include a guidewire 5102 having a core wire 5104 witha groove 5110 for the optical fiber 5112.

Like the fiber pressure sensor assembly 5000 of FIG. 50, the core wire5104 disposed within the slotted tube 5106 in FIG. 51 can bediscontinuous along a length of the slotted tube 5106. The optical fiber5112 between the proximal grooved solid core wire 5104 and the sensorhousing 5114 can be allowed to freely locate within the slotted tube5106, can be attached to the slotted tube 5106, can be protected furtherwith a thicker coating or a suitable tubular member, can be wound arounda thin core wire (not depicted), or can be provided with other suitableconstruction means. Additionally, as seen in the example configurationin FIG. 51, the distal core wire 5116 (and/or shaping ribbon) can bedecoupled from the sensor housing 5114 containing sensor 5115, andsecurely and separately attached to the slotted tube 5106 and distalcoil 5108.

FIG. 52 depicts another example of a guidewire in combination with anoptical fiber pressure sensor assembly that can be used to implementvarious techniques of this disclosure. FIG. 52 depicts a fiber pressuresensor assembly 5200, such as described above in numerous exampleconfigurations. As described in detail above, the fiber pressure sensorassembly 5200 can include a guidewire 5202 having a core wire 5204.

Like the example configuration depicted in FIG. 49, the fiber pressuresensor assembly 5200 of FIG. 52 includes a proximal slotted tube 5206having a plurality of slots 5207 along its length. Proximally, theslotted tube 5206 can be attached to the core wire utilizing adhesive,solder, welding, or other suitable techniques.

In contrast to the fiber pressure sensor assembly designs shown anddescribed in FIGS. 49-51, the sensor housing 5214, and thus the sensor5215, can be moved along a length of the slotted tube 5206. In theexample configuration shown in FIG. 52, the assembly 5200 can include atube 5230, e.g., coaxially positioned, extending along a length of ahollow core wire 5204. The tube 5230 can be attached to the sensorhousing 5214 and can contain the optical fiber (not depicted in FIG.52). The tube 5230 can be constructed of metal or plastic, for example.Although not depicted, in some example configurations, the tube 5230 caninclude a slot extending along at least a portion of its length, e.g.,straight or spirally formed, to accommodate the facile side loading ofthe optical fiber along its length.

One advantage of the assembly 5200 is that the guidewire 5202 can bepositioned initially with its distal tip 5232 in a distal vessel and thesensor 5215 distal to a lesion. Without moving the guidewire 5202, auser, e.g., a clinician, can move the sensor 5215 from a position thatis distal of the lesion to a position that is proximal of the lesion todetermine if there has been any drift of the sensor 5215 and therebyverify that an FFR calibration is accurate. With current devices, theposition of the sensor 5215 is fixed and, as such, a clinician needs tomove the entire guidewire 5202 so that the sensor is proximal to thelesion to verify that an FFR calibration is accurate.

FIG. 53 depicts an example of an optical connector that can be used toimplement various techniques of this disclosure. More particularly, FIG.53 depicts an optical connector 5300 that can be positioned at aproximal end of the assembly 5200 of FIG. 52, for example. The opticalconnector 5300 of FIG. 53 can include a housing 5302 and a controlmechanism 5304 coupled to the housing 5302 and to a portion of aproximal end region 5306 of the tube 5230 of FIG. 52 that is positionedwithin the hollow guidewire 5202 of FIG. 52. When advanced distally orretracted proximally, e.g., using a thumb tab 5308, along a length ofthe optical connector 5300, for example, the control mechanism 5304 canslideably adjust a longitudinal position of the tube 5230 of FIG. 52, anoptical fiber (not depicted), and the sensor housing 5214 of FIG. 52attached to the tube 5230. In this manner, the sensor 5215 of theassembly 5200 can be moved along a length of the fiber pressure sensorassembly 5200.

In addition to the alignment improvement techniques described above withrespect to FIGS. 29A and 29B, the present inventors have recognized thatit can be desirable to utilize fusion splicing techniques in order toachieve a high precision alignment of optical fibers. An exampletechnique is described below with respect to FIGS. 55A and 55B.

FIG. 54 depicts an example of a fusion splice between two opticalfibers. In FIG. 54, a 25 micrometer outer diameter single mode opticalfiber 5400 is spliced to a 125 micrometer outer diameter single modeoptical fiber 5402. Generally speaking, an end of the 25 micrometeroptical fiber 5400 and an end of the 125 micrometer optical fiber 5402may be heated and softened through one or more heating cycles generatedby a fusion splicing system. Once the ends of the two optical fibers5400, 5402 are sufficiently viscous, the two ends may be pushed togetherwhereby their surface tensions of the two materials join together. Asolid joint between the two fibers is created after the fibers arecooled.

Additionally, mode field diameters may or may not be matched. The outerdiameters listed above are for example purposes only. Other outerdiameter combinations may also be useful. The fusion splicing techniquecan also be applied to multimode optical fibers. Fusion splicing may beaccomplished using a laser based fusion splicing system, such as theLZM-100 splicing system available from AFL Corporation.

FIGS. 55A and 55B show an example of a proximal region of a guidewireassembly 5500, such as one of the various guidewire assemblies describedherein, terminating at a proximal end connector 5502. FIG. 55B shows anenlarged region of FIG. 55A. FIGS. 55A and 55B will be describedtogether for purposes of conciseness.

Like in FIG. 29A, the guidewire assembly 5500 can include a helicallywound optical fiber 2402 that can be located in a helical groove 2712along the guidewire body. The proximal end connector 5502 can includeseparable portions: (1) a distal portion that can include a metal orother tube 2904 (also referred to as a tubular coupler) having aninterior lumen diameter that can be attached to both the outer diameterof the body of the proximal region of the guidewire assembly 5500 andthe outer diameter of a ceramic or other distal ferrule 5506 such thatthe optical fiber 2402 can extend from a periphery of the guidewire bodyto and through a center axis lumen of the distal ferrule 5506; and (2) aproximal portion that can include a connector housing 2908 carrying aceramic or other proximal ferrule 5510, a split sleeve ferrule guide5508, and a distal receptacle guide 2914 that can provide a taperedportion into which a portion of the distal ferrule 5506 and the metaltube 2904 can be received. In some example configurations, the distalreceptacle guide 2914 can extend distally to encompass a proximalportion of the core wire of the guidewire assembly 5500.

In contrast to the technique depicted in FIG. 29A in which the proximalend of the distal ferrule 2906 defined a narrow channel that allowed theoptical fiber 2402 to align with and butt against the optical fiber 2916in the proximal ferrule 2910, FIGS. 55A and 55B depict the optical fiber2402 fusion spliced to a short length of optical fiber 5512, e.g., 125micrometers outer diameter, which is aligned with and butts against theoptical fiber 2916. The short length of optical fiber 5512 (or “opticalfiber stub 5512”) can have a larger outer diameter than optical fiber2402, with minimal optical losses. The spliced short segment opticalfiber 5512 can have a diameter suitable to allow precision alignmentwith a proximal ferrule 5510.

Terminating the smaller diameter optical fiber 2402 into a largerdiameter short length of optical fiber 5512 by fusion splicing mayovercome the difficulty in terminating the smaller optical fiber 2402,e.g., 25 micrometers outer diameter, with high accuracy, e.g., with 1micrometer accuracy, with optical fiber 2916. By fusion splicing theoptical fiber 2402 to the short length of optical fiber 5512, thecombination of the optical fiber 2402 and the short length of opticalfiber 5512 can be positioned into the ferrule 5506 at the proximal endof the guide wire, polished, and mated to optical fiber 2916 on theother side of the connector 5502.

FIGS. 56A and 56B show an example of a proximal region of a guidewireassembly 5600, such as one of the various guidewire assemblies describedherein, terminating at a proximal end connector 5602. FIG. 56B shows anenlarged region of FIG. 56A. FIGS. 56A and 56B will be describedtogether for purposes of conciseness.

In contrast to the alignment techniques described above with respect toFIGS. 55A and 55B that used fusion splicing, the present inventors havealso recognized that capillary tubes, e.g., high precision silica orother suitable material, may be disposed about the reduced outerdiameter optical fiber 2402, e.g., 25 micrometer outer diameter, toincrease the outer diameter such that a standard size ferrule or lowercost alignment device may be utilized. The capillary tube can be sizedand shaped to be securely disposed about a proximal portion of theoptical fiber.

In the example configuration shown FIGS. 56A and 56B, a reduced diameteroptical fiber 2402, e.g., 25 micrometer outer diameter, can be placedinside a capillary tube 5605 (or “tubular member” 5605), e.g., silica orborosilicate tubing, with dimensions of 125 micrometer outer diameterand about 25.5 um inner diameter. The reduced diameter optical fiber2402 and capillary tube 5605 may be bonded, as necessary, e.g., epoxybonded or fusion bonded. The combined assembly may then be bonded to aferrule 5606, e.g., alumina or other suitable material, with arelatively large inner diameter, e.g., an inner diameter of 125micrometer. The ferrule can be sized and shaped to be securely disposedabout the tubular member 5605. This approach can allow standardconnection techniques to be achieved with lower cost ferrules.

FIG. 56C show another example of a proximal region of a guidewireassembly 5600, such as one of the various guidewire assemblies describedherein, terminating at a proximal end connector 5602. FIG. 56C shows analternative connector for use with any of the guidewires or sensorsdescribed in this disclosure. Similar connection techniques can be foundin U.S. Pat. No. 8,583,218 to Michael J. Eberle, which is incorporatedherein by reference in its entirety. The connection surfaces can beformed by cutting through a guidewire assembly 5608 with a thin dicingblade at a slot 5610, thereby creating mirror image interfaces. Usingthis technique, the positioning of the optical fiber or fibers is notcritical.

A reduced size optical fiber can extend through a tubing or thin walleddeformable metal tube 5614, as seen in FIG. 56D, and into the connector5612, e.g., lead, of FIG. 56C. Within the metal tube 5614, the reducedsize optical fiber 5616 can be encapsulated in a suitable material thatcan also contain filler materials 5618, such as glass bead, glass fibersor other fillers that can modify the physical properties of theencapsulant so that optimized dicing, polishing and connection can beachieved.

The reduced size optical fiber can alternatively be spliced to a largerfiber proximal to the dicing cut or alternatively within the leadsection. The reduced size optical fiber can alternatively be fusionspliced to a larger optical fiber distal to the deformable metal tube orwithin the deformable metal tube and the dicing cut can be made throughthe section of the larger fiber 5616 for improved connectionreliability.

Alternatively, the reduced size optical fiber may be spliced to a largeroptical fiber within the deformable metal tube and the dicing cut can bemade at the splice between the reduced size optical fiber and the largerfiber, yielding a small fiber to large fiber interface that is properlyaligned. In the preceding examples, the dicing cut may be madeorthogonal to the axis of the reduced size or larger optical fibers oralternatively at an angle to the axis to optimize connection reliabilityor to minimize optical reflections as appropriate.

Many of the assemblies described above can include a groove formed alongthe length of the guidewire core, e.g., groove 2712 of FIG. 56A, intowhich an optical fiber may be positioned. In some exampleconfigurations, e.g., FIG. 27, the groove extends along a taperedsection of the core wire. The present inventors have recognized that thegroove along the tapered section of the core wire can be advantageouslycreated while the core wire material is at its original, constantdiameter (pre-tapering). A specialized fixture to accommodate a reduceddiameter core wire may not be needed if the core wire has a constantdiameter. As described below with respect to FIGS. 57A and 57B, thepresent inventors have recognized that the groove may be formed in thecore wire material before it is further processed by, for example,centerless grinding. In this manner, a lower cost component may beachieved with a high quality groove.

FIGS. 57A and 57B depict an example of a technique for forming a grooveinto the raw material of the core wire as part of the drawing processfor the core wire. FIG. 57A depicts a portion of core wire 5700 defininga groove 5702 extending along a length of the core wire 5700. The groove5702 can be made by removing material of the core wire 5700 to a firstdepth along a length of the core wire. The groove 5702 can be suitablefor use along the majority of the length of the guidewire withoutfurther processing. The groove 5702 may also be formed with or without aspiral component. In accordance with this disclosure, a section of thecore wire length for tapering can be identified, e.g., section 5704 inFIG. 57A. Next, using techniques including, but not limited to,micromachining, laser, electric discharge machining (EDM), dicingtechniques, etc., the manufactured groove 5702 in the section 5704 canbe made deeper, as shown at 5706 in FIG. 57A. The deeper groove 5706 canhave one or more depths, e.g., a second depth deeper than the firstdepth of the groove 5702, or may have a tapered depth along its length.In some example configurations, the deeper groove may be straight and/orspiral cut.

Once the deeper groove 5706 is accomplished, the core wire 5700 may thenbe centerless ground or otherwise processed to remove material andreduce its diameter while preserving some or all of the deeper groove5704 as required, as seen in FIG. 57B. The tapered section may allow theoptical fiber to fit under a coil, e.g., proximal spring coil region2504 of FIG. 27, without being pinched or other restricted by the coil.

In some example implementations, the core wire 5700 of FIG. 57B can bemanufactured using precision 3D printing techniques.

The present inventors have also recognized that it may be desirable toachieve a robust proximal optical connector on the guidewire that can bemated to the lead assembly reliably and often. To that end, the presentinventors have recognized that it may be desirable to accommodatesignificant linear force to the optical fiber and ferrule such that theoptical fiber of the guidewire is maintained in close contact with theoptical fiber of the lead. Additionally, the present inventors haverecognized that a relatively simple assembly process is desirable, aswell as low cost and, if desired, no requirement for a groove to beformed in the tapered section of the proximal core wire. The presentinventors have determined that these features can be achieved byimplementing the assembly shown and described below with respect toFIGS. 58A-58B.

FIGS. 58A-58B depict an example of a proximal region of a guidewireassembly, terminating at a proximal end connector. FIG. 58B is across-sectional side view of the assembly of FIG. 58A. FIGS. 58A-58Bwill be described together for purposes of conciseness.

In FIG. 58A, a tubular member 5800 can form a support between theproximal core wire 5802 and the ferrule 5510 such that significantlinear force is accommodated without disturbance of the adhesives oroptical fiber 2402. The tubular member 5800 defines a slot 5805 that canaccommodate the optical fiber 2402 over the transition from the groove2712 along the outer diameter of the core wire 5802 to the central lumenof the ferrule 5510 without the addition of a groove along the taperedsection of the proximal core wire 5802 (as in FIG. 29A, for example).The slot 5805 of the tubular member 5800 and the tapered core wire 5802can allow the optical fiber 2402 to be routed from the groove 2712 thatextends along the outside diameter of the core wire 5802 and brought toa coaxial position such that the optical fiber 2402 is coaxial with theassembly proximally and can enter the connector 5802 coaxially. As seenin FIG. 58B, a metal or other tube 2904 (also referred to as a tubularcoupler) can then be placed around the tubular member 5800 to secure theassembly together.

In some example implementations, the tubular member 5800, ferrule 5510,and the core wire 5802 contact one another such that a push on theferrule 5510 pushes the tubular member 5800, but a push on the core wire5802 does not displace the ferrule 5510. In this manner, theconfiguration in FIGS. 58A-58B can result in a solid, robust designwithout the need for an adhesive as a primary strength member (althoughan adhesive may still be used in the assembly process generally). Insummary, instead of creating a groove in the proximal region of the corewire 5802, the design in FIGS. 58A-58B utilizes a slot 5805 in thetubular member 5800 so that the optical fiber 2402 can be located withinthe slot 5805 until the core wire 5802 has a diameter small enough thatno slot is needed.

The present inventors have also recognized that optical sensorassemblies of the type described throughout this disclosure may exhibitvariations in characteristics due to variations in the raw components,assembly techniques, manufacturing processes or tolerances, etc. Thesetypes of variations can be corrected for during use of the devices byproviding characteristic data to an external instrument, e.g.,controller 602 of FIG. 6A, that controls the device laser light sources,optical components, and measurement and control circuitry.

For example, imaging and physiologic measurement devices have previouslybeen marketed since the mid-1990s where the characteristic data wassupplied in the form of trim resistors, digital data stored in EPROMS,and, more recently, RFID chips or other forms of memory, with each setof data being unique to the device in use. The data set can be stored indevice characteristic module that is attached to or separate from thedevice, and may include information relating to characteristics such assensitivity, calibration, operating wavelength or may include deviceidentifying serial number or equivalent. Alternatively or additionly,characteristic data may be stored on a connected or accessible localserver or in the cloud.

As described in detail above with respect to FIGS. 6A-6B, one or moretechniques of this disclosure can remove and/or compensate for theeffects of temperature drifts and other deleterious effects that mightcompromise the accuracy of the pressure reading. For example,polarization scrambling techniques, ambient temperature nullingtechniques, laser tracking techniques, and laser temperature monitoringtechniques can be used in combination to correct for temperature driftsthat can affect the accuracy of the pressure readings. As describedabove and shown in FIG. 6B, the present inventors have recognized thatit may be desirable in some example implementations to include twolasers in the laser tracking system in order to provide the ambienttemperature nulling techniques, laser tracking techniques, and lasertemperature monitoring techniques, for example. As such, in the exampleconfiguration shown and described below with respect to FIG. 59, foreach laser, a controller, optical detector, and optical locking setpoint, zero pressure DC offset value, and gain value can be provided.

In addition and as described in more detail below with respect to FIG.59, the present inventors have recognized that sensors and systemsformed using various techniques described in this disclosure may includelaser diodes with varying operating characteristics. By way of example,the described method of detecting pressure may include a modulation of alaser diode current to track an operating wavelength. Laser diodes fromvarious manufacturers, or within lots from the same manufacturer, mayexhibit different characteristics. In response to the modulation of thelaser diode current, the laser may, to varying degrees, also exhibitcorresponding or related variation in the laser optical output power.This variation in power may contribute to noise or uncertainty about thepressure measurement and, therefore, it may be desirable to reduce oreliminate it.

The present inventors have recognized that the output power variationcan be regulated by variable optical attenuators (VOAs), e.g., anoptical power regulator, with feedback loops, which can stabilize theoutput power of a laser. It may be further desirable to implement theVOAs in each of the optical pathways for every laser, e.g. for thetemperature sensing laser and the temperature/pressure sensing laser.

FIG. 59 is a block diagram of another example of a laser trackingsystem, in accordance with this disclosure. In FIG. 59, for each laser,a controller, optical detector, and optical locking set point, zeropressure DC offset value, and gain value can be provided. Many of thecomponents in FIG. 59 were described above with respect to FIGS. 6A and6B and, for purposes of conciseness, will not be described again. Likenumerals having different letter suffixes in FIG. 59 may representdifferent instances of similar components in FIGS. 6A and 6B. Forexample, laser controllers 602A, 602B of FIG. 59 represent differentinstances of controller 602 of FIG. 6A, optical detectors 608A, 608B ofFIG. 59 represent different instances of optical detector 608 of FIG.6A, etc.

As mentioned above and in accordance with this disclosure, FIG. 59 alsoincludes two VOAs, namely VOA 1 5900A and VOA 2 5900B (referred tocollectively in this disclosure as VOAs 5900). VOA 1 5900A and VOA 25900B receive an output from the laser 1 630 and the laser 2 640,respectively. The VOAs 5900 can help stabilize the optical powerinjected into the system from each of the lasers 630, 640 via feedbackpaths 5902A, 5902B. The VOAs 5900 can help maintain a constant level ofoptical power output by each of the lasers 630, 640, despite any changesin conditions, e.g., changes in pressure, changes in insertion loss,optical tracking.

The addition of the VOAs 5900A, 5900B can have the added benefit thatthey remove changes in the optical output power caused by changes to thedrive current of the lasers 630, 640 to facilitate optical insertionloss monitoring. When the lasers are dithered to generate the tone forinsertion loss monitoring (FIG. 33), there can also be an associatedoptical power variation that may need to be subtracted from theinsertion loss signal before an accurate value can be calculated. Thiscan be eliminated, however, if the VOAs are chosen to respond withsufficient bandwidth.

Described above with respect to FIGS. 30-33 are techniques that candynamically adjust a locking level to account for any changes in opticalinsertion loss. There are other techniques that may be applied toachieve a similar result. For example, another technique to account forinsertion loss can utilize passive correction, as described in FIG. 65.

FIG. 65 is a flow diagram illustrating another example of a method 6500for compensating for optical insertion loss in an optical pressuresensor using various techniques of this disclosure. The compensationtechnique of FIG. 65 is a passive correction technique in that there isno dynamic correction of the locking level, but instead a scaling of thedither tone by at least one first order coefficient and possibly higherorder polynomial correction factor. The result of this scaling can beadded or subtracted from the apparent pressure reading to give thecorrect value. As seen in FIG. 65, the VOAs, e.g., VOAs 5900A, 5900B ofFIG. 59, can be set to a fixed value (block 6502) and a dithergenerator, e.g., AC dither generator 3312 of FIG. 33, can apply a dithersignal to the laser controllers, e.g., laser controllers 602A, 602B ofFIG. 59 (block 6504). The laser controllers can measure and normalizethe dither signal (block 6506) and multiply the normalized dither signalby the slope coefficient(s), e g., first and second order coefficients(block 6508). The resulting correction value can then be applied to,e.g., added to or subtracted from, the pressure signal (block 6510).Finally, the laser controllers can continue to measure the dither signal(block 6512) and apply the determined correction, as needed, to thepressure signal (block 6510).

The technique of FIG. 65 can be suitable for small changes in theinsertion loss but may not be sufficiently accurate for large changes.It can also be desirable to ensure that the scaling coefficients arevery accurate. The scaling factor can be dependent on the slope of theoptical filter Fabry-Perot. An accurate scaling factor can be achievedby using a dynamic normalization at the start of the measurement. Thiscan involve normalizing the signal generated by the dither tone andscaling by a known slope factor that was factory determined for thatparticular pressure sensing device. Alternatively, a direct measure ofthe optical slope can be determined if the laser is dithered by a knownamount.

FIG. 66 is a flow diagram illustrating another example of a method 6600for compensating for optical insertion loss in an optical pressuresensor using various techniques of this disclosure. The technique shownin FIG. 66 does not depend on having very accurate slope coefficientsand can offer extended dynamic range to account for insertion losschanges. This technique can use the VOAs 5900A, 5900B in a feedbackloop. For example, a dither generator, e.g., AC dither generator 3312 ofFIG. 33, can apply a dither signal to the laser controllers, e.g., lasercontrollers 602A, 602B of FIG. 59 (block 6602). The VOAs, e.g., VOAs5900A, 5900B of FIG. 59, can be set to a starting value (block 6604).The laser controllers 602A, 602B can monitor the insertion loss dithertone and use electronic feedback to the VOAs 5900A, 5900B to maintainthe tone at a fixed level. The laser controllers 602A, 602B can measureand normalize the dither signal (block 6606), wait a predeterminedsample period (block 6608), and measure a new dither signal (6610). Ifthere is a difference between the new dither signal and the normalizeddither signal (“YES” branch of block 6612), then the laser controllers602A, 602B can adjust the VOAs 5900A, 5900B to restore the originaldither signal (block 6614). If there is no difference between the newdither signal and the normalized dither signal (“NO” branch of block6612), then the laser controllers 602A, 602B can again measure thedither signal (block 6610).

Under normal insertion loss conditions, the VOAs can be operated in amanner such that there is a reserve of optical power, e.g., the VOAs areoperating in a lossy state. As the insertion loss of the system changes,the dither tone will likely also change. The VOAs can be adjusted tobring the dither tone back to the original value. For instance, if theinsertion loss of the optical system increased, then the VOAscan beadjusted to allow more light into the system, thereby preserving themagnitude of the dither tone.

The opposite is also true. If the insertion loss of the optical systemdecreased, the VOAs can be adjusted to allow less light into the system,thereby preserving the magnitude of the dither tone. The advantage ofthis method is that accurate scaling coefficients are not needed as inthe passive correction technique described above, and there is no needto dynamically adjust the locking level because the relative opticalshape of the filter is not changed. It also has the advantage of muchbetter dynamic range as compared to the other techniques, only limitedby the dynamic range of the VOAs. Another benefit is that the opticalpower at the sensor is kept constant thereby avoiding any changes in theoptical self heating effects within the sensor.

In addition, the system of FIG. 59 can include a wavelength multiplexer5904, which can couple a first wavelength from the laser 630 and asecond wavelength from the laser 640 to the same optical fiber. Thecoupled wavelengths can be output to a polarization scrambler 5906,e.g., a series of “optical waveplates” physically located between wherethe laser beams exit lasers 602A, 602B and the FBGs of the optical fiberpressure sensor device. As described in detail above, the polarizationscrambler 5906 can be used to scramble or average a range ofpolarization states so the final result is not biased to any givencombination of birefringent axis of the FBG and incident polarizationstate. In this manner, the polarization scrambler 5906 can overcome theeffects of birefringence and determine a true pressure reading. Thesystem of FIG. 59 can also include a wavelength demultiplexer 5908 thatcan separate a light beam reflected from the pressures sensor device5910 into its constituent wavelengths, which can then be detected byoptical detectors 608A, 608B and be used to generate a pressure reading.

This disclosure describes various methods of forming optical pressuresensors. In some example implementations, these methods includeassembling sensors utilizing epoxy bonds of the fiber to the surroundingapparatus. For example, as described above with respect to FIG. 38, theoptical fiber 3802 can be securely affixed to the proximal housingportion 3806 via an epoxy 3812, and the optical fiber 3802 can besecurely affixed to the distal housing portion 3804 via an epoxy 3816.The present inventors have recognized, however, that the use of theepoxy bonds can cause variations in sensors and, to some extent,unpredictable behavior of the sensors. Thus, in some exampleconfigurations, it can be desirable to eliminate epoxy as the method ofattaching the optical fiber to the sensor apparatus.

As described below with respect to FIG. 60, the present inventors haverecognized that it can be desirable in some implementations to constructa sensor assembly, e.g., pressure sensor assembly 3800, without theepoxy bond by creating fusion bonds of the optical fiber glass directlyto the glass of the sensor housing. Such bonds can be accomplished byway of laser fusion bonding utilizing, for example, a laser based fusionsplicing system, such as the LZM-100 splicing system available from AFLCorporation.

FIG. 60 depicts another example of a portion of a pressure sensorassembly 6000. Many of the components shown in FIG. 60 are similar tothose described above with respect to FIG. 38 and, for purposes ofconciseness, will not be described again. As mentioned above, however,the assembly 6000 can be fusion bonded together without the use of theepoxy, e.g., epoxy 3812, 3816, utilized in the example of an assemblyshown in FIG. 38.

For example, the proximal end 3810 of the housing 3806 can be neckeddown around the optical fiber 3802, thereby reducing or eliminating theneed for epoxy, e.g., epoxy 3812 of FIG. 38. In one example, a smallsection 6002 of the proximal end 3810 can be heated and, when pulled,the section 6002 necks down around the optical fiber 3802. In anotherexample, a small section 6002 of the proximal end 3810 can be heated anda vacuum can be applied to pull it down around the optical fiber 3802.As the section 6002 of the proximal end 3810 of the housing 3806 isheated, the heat can transfer through the section of the housing 3806and heat an adjacent section of the optical fiber 3802, which has anouter diameter that closely matches the inner diameter of the housing3806. Once the optical fiber 3802 is sufficiently heated, the opticalfiber 3802 (glass) and the housing 3806 (glass) in the heated regionwill be fusion bonded together.

FIGS. 61A and 61B depict another example of a portion of a pressuresensor assembly 6100. FIG. 61B depicts an enlarged region of FIG. 61A.FIGS. 61A and 61B will be described together. Many of the componentsshown in FIGS. 61A and 61B are similar to those described above withrespect to FIGS. 38 and 60 and, for purposes of conciseness, will not bedescribed again.

As described above with respect to FIG. 38, the sensor membrane of thewindow 3808 located between the distal and proximal portions 3804, 3806can be formed of silicone in some example configurations. Silicone,however, may not be sufficiently linear for some sensor applications.The present inventors have recognized that it may be desirable for thesensor membrane of the window to behave as linearly as possible.

In the example depicted in FIGS. 61A and 61B, the window 6108 caninclude a thin-walled bellows-shaped sensor membrane 6110. In oneexample implementation, the bellows-shaped sensor membrane 6110 can bemade of silicon, which exhibits linear elasticity (like a spring), incontrast to silicone. In another example implantation, thebellows-shaped sensor membrane 6110 can be made of a metal that exhibitslinear elasticity. In another example implantation, the bellows-shapedsensor membrane 6110 can be made of fused silica, which also exhibitslinear elasticity. Other materials exhibiting linear elasticity arepossible and are considered within the scope of this disclosure.

In some example implementations, one or more components of the opticalpressure sensor assembly 6100 of FIGS. 61A and 61B can be manufacturedusing precision 3D printing techniques. For example, fused silica, orother transparent materials, can be exposed using high power laserlight, e.g., highly focused high power pulsed laser light. In certainmaterials, substrates exposed can be etched using hydrofluoric acid (HFacid), which reacts more quickly with the exposed regions than with theunexposed regions. Using this technique, the sensor housing and sensormembrane can be manufactured from a single substrate, or multiplecomponents can be manufactured separately and then assembled. A systemand method for achieving this technique is available from Femtoprint(www.femtoprint.eu/).

The present inventors have also recognized that the pressure sensorsdescribed in this disclosure can be enhanced by reducing the diameter ofthe optical fiber in select regions, for example, FBG 1 of FIGS. 38, 60,and 61A, or a portion thereof, to increase the overall pressuresensitivity of the device. The diameter reduction can be achieved by,for example, selectively exposing the region to HF acid. In otherexamples, the pressure sensors described in this disclosure can beenhanced by reducing the diameter of the optical fiber in, for example,FBG 2 of FIGS. 38, 60, and 61A, or a portion thereof. In anotherexample, the pressure sensors described in this disclosure can beenhanced by reducing the diameter of the optical fiber in, for example,both FBG 1 and FBG 2 of FIGS. 38, 60, and 61A, or a portion thereof.

The present inventors have also recognized that the pressure sensorsdescribed throughout this disclosure can be coated with one or moretherapeutic agents, e.g., an anti-thrombotic agent. Additionally oralternatively, the present inventors have also recognized that thepressure sensors described throughout this disclosure can be coated withone or more lubricious coatings, e.g., hydrophilic and/or hydrophobiccoating materials. In some examples, the sensor cavity of the pressuresensor, e.g., the space surrounding the sensor housing and the distalFBG, can be filled with a gel or oil, e.g., a biocompatible gel or oil,which can protect the pressure sensor and help prevent the trapping ofbubbles.

In computing an FFR value, the proximal aortic pressure (proximal to astenosis) is normally measured by a dedicated fluid coupled transducerattached in fluid communication with the guide catheter, which can thenmeasure a proximal aortic pressure when attached to an installed patientmonitoring system. This pressure measurement can then be providedelectronically to the dedicated FFR instrument. The present inventorshave recognized that an advantageous pressure sensing instrument can beachieved by providing a dedicated fluid coupled pressure sensor inseries with the pressure sensor utilized by the patient monitoringsystem of the catheterization laboratory, as described below withrespect to FIG. 62.

FIG. 62 is a block diagram of an example pressure sensing system 6200,in accordance with this disclosure. One FFR computation approach canutilize electronic communication between a patient monitoring system6202 of the catheterization laboratory and a dedicated pressure system6204. For example, one FFR computation approach can utilize electroniccommunication of either a Pd pressure measurement (the pressure distalto the stenosis) from the dedicated pressure system to the patientmonitoring system, or a Pa pressure measurement (the pressure proximalto the stenosis) from the patient monitoring system to the dedicatedpressure system, where FFR=Pd/Pa. In contrast to these approaches, thepressure sensing system 6200 of FIG. 62 can allow the pressure system6204 to compute an FFR value without electronically communicating eithera value of Pd or a value of Pa between the patient monitoring system6202 and the pressure system 6204, e.g., a standalone computation.

As seen in FIG. 62, a guidewire system including a pressure sensingguidewire 6205 (e.g., the optical pressure sensor assembly 3800 of FIG.38, any of the numerous other optical pressure sensor assembliesdescribed in this disclosure, or any existing pressure sensingguidewires) can sense the Pd pressure. The guidewire 6205 can transmit asignal representing the Pd pressure via a connector 6208 and an opticalfiber or wire 6210 to the pressure system 6204.

A guide catheter system including a guide catheter 6206 can be in fluidcommunication with a pressure sensor 6212 utilized by the patientmonitoring system 6202. The pressure sensor 6212 can determine a firstPa pressure measurement and transmit the determined first Pa pressuremeasurement via wire 6214 to the patient monitoring system 6202.

In accordance with this disclosure, a dedicated second external pressuresensor or (“external transducer”) 6216 can be fluid coupled in serieswith the pressure sensor 6212 utilized by the patient monitoring system6202. Sensors 6216 and 6212 can be arranged to be closely coupled andplaced at the same height in relation to the patient. The dedicatedpressure sensor 6216 can determine a second identical Pa pressuremeasurement and transmit the determined second Pa pressure measurementvia a wire 6218 to the pressure system 6204. Then, the pressure system6204 can compute an FFR based on the received Pa and Pd measurementsusing an FFR circuitry or module 6220. In this manner, communication ofPa (or Pd) pressure measurements between the patient monitoring system6202 and the patient system 6204 can be eliminated. As such, thisapproach can simplify the design of the instrument and minimize thenecessity to supply any dedicated electronic connections. Further, thisapproach can provide greater electrical isolation and patient safety.

Pressure system 6204 can take different forms. For example, pressuresystem 6204 can be a stand-alone battery powered or mains poweredconsole with connections solely to the external transducer 6216 by thewire (or other connector) 6218 along with optical fiber or wire 6210connecting console 6204 to the guidewire (or “sensing device”) 6205. Forsome sensors, applications or configurations, the wire 6218 may beunnecessary. Alternatively, pressure system 6204 (also referred to inthis disclosure as “console 6204”) can be a module in a larger consoledesigned to accommodate other instrumentation, sensing mechanisms,imaging mechanisms, treatment mechanisms or other suitable functions.Alternatively, console 6204 can be a sensing system other than apressure sensing system similarly achieved by a stand-alone console oran integrated module as described above.

Console 6204 can be capable of stand-alone measurement and diagnosticfunctionality through various outputs or display of data for the enduser, such as through screen displays, numeric displays, portable memorytransportation, printer outputs and the like. Alternatively orinclusively, console 6204 can provide signals that communicate relevantdata to other instruments. Signals can include analog or digitalsignals, which can conform to various standards or can be unique to theinstrument, for passage to other instruments via suitable means.Suitable means can include, RF, Bluetooth or Wi-Fi signals or similar,as well as custom cables, Ethernet cables, electrical cables or fiberoptic cables or similar.

Console 6204 can provide data or signals that can be provided tomultiple function instruments via connection or integration therein. Thedata can be displayed separately or in combination with othermeasurements or 2D or 3D images in real-time or through memory means forsubsequent display, analysis or processing. By way of further example,pressure measurement data can be provided to imaging systems such thatthe pressure readings can be coregistered to the images of, for example,coronary or other blood vessels in such a way as the physician can seethe variation in pressure along the image of the blood vessel. Theimages can be provided by fluoroscopy, x-rays, IVUS or OCT or similar.The pressure guidewire 6205 can also incorporate sensors, transponders,visual characteristics, x-ray opacity or other means that can assist inthe coregistration of the pressure data on the images. Coregistrationcan be accomplished by detection or processing of the coregistrationinformation through electronic or software means. Coregistration can beapplied to other sensor forms or multiple sensors in parallel orserially. Data provided or displayed can be stored as part of thepatient record through printout, electronic, or other means.

The console 6204 can provide data that is used to guide treatment, suchas FFR. Data can be provided in multiple formats either raw or inprocessed or calibrated form. Data can be used for decision making abouttreatment strategies, cost control strategies, or short or long termoutcome strategies. Data can be generated at one point in a treatmentprocedure or at multiple times throughout a procedure. Multiplemeasurements can be placed in the patient record. Data can be generatedin various clinical settings or patient physiologic conditions. Data canbe generated in combination with the administration of a drug, during adiagnostic procedure or during a treatment procedure.

The console 6204 can provide data that is used to guide or directlycontrol other treatment instruments or devices. Data or signals derivedfrom sensors can be used, for example, to control blood infusion pumps,balloon pumps or other life support instruments or devices. Data orsignals can be used to guide or control tissue or blood modification orremoval instruments. Data or signals can be used to turn on or turn offtreatment devices and instruments, synchronize their functionality orincrease or decrease their functionality. Instruments or devices caninclude atherectomy or aspiration devices, laser ablation devices,electrical devices or any other suitable device.

The console 6204 can be located close to the patient or remotely. Theconsole 6204 can incorporate control functions, user interfaces,dedicated or touch controls, software control algorithms and similar.The console 6204 can be controlled directly or remotely through anelectrical or optical control, infra-red or wireless control. Theconsole 6204 can support multiple displays of data, for example,multiple pressure signal screens at various locations.

In another example of the invention described herein, the guidewire 6205can be provided with the incorporated sensor functionality which can beactivated if the procedure requires the sensing measurement to be made.For example, the guidewire 6205 is a high performance guidewire withintegrated highly miniaturized pressure sensing capability. In oneexample, the cost of integration of the pressure sensing capability isminimal compared with the cost of providing the guidewire. The guidewire6205 can be provided to the physician with the option of activating thesensor at any time through the procedure. The optical fiber or wire (orother connection) 6210 can be provided as a separate device, whichenables a separate charge to be made for the sensing measurement only ifthe measurement is deemed necessary. In this manner, the physician doesnot have to commit to the cost of the sensing measurement in advance ofthe procedure. In this example, the connector 6208 is universal for theoperation of any sensing guidewire 6205 with the optical fiber or wire6210. In an alternative example, the sensing guidewire 6205 is providedwith a unique characteristic module. The characteristic module can be alow cost disposable storage data device that can be necessary to operateor calibrate the sensing guidewire 6205 and can be used if the physiciandecided to activate the measurement functionality of guidewire 6205. Thecharacteristic module can be any suitable form of device, such as amemory stick, RFID device or similar. In operation, the characteristicmodule can be in communication with the console 6204, and the console6204 can adjust the operation or calibration of the guidewire 6205 inorder to provide an accurate sensing measurement.

By way of another example, the characteristic module can contain aunique identifier, such as a serial number or similar, that iscommunicated to the console 6204. The console 6204 can incorporatememory such that the serial number is recorded upon first use, or it maybe connected to a data base through wireless, Ethernet, internet orother means, to verify the device has not been used previously, and isprohibited from being used at a later time or for another patient.Alternatively, the optical fiber or wire (or other connection) 6210 canincorporate the same or a different unique identifier such that it canbe prevented from being used a second time.

As can be appreciated from this arrangement, a low cost, highperformance guidewire can be provided with on board sensor readyconfiguration that can be activated at the command of the physician bypurchasing and using a separate optical fiber or wire (or otherconnection) 6210. This arrangement can help minimize concern over thechoice of an expensive sensing guidewire in advance of the knowledge ofthe merits of the sensing measurement. In addition, by way of a furtherexample, second fluid pressure sensor 6216 and wire 6218 can be providedtogether with the optical fiber or wire (or other connection) 6210.Second pressure sensor 6216 can be a single use pressure sensor.

Alternatively, guidewire 6205 and connection means 6210 can be providedtogether as matching sets together with or separately from externalsensor 6216. Connection means 6210 may also incorporate thecharacteristic module described herein, or it may be providedseparately.

FIG. 67A is side view of another example of a pressure sensor housing,in accordance with this disclosure. FIG. 67A depicts a main housing 6700having a diaphragm 6702 at an end 6704, an optical fiber 6706 enteringthe main housing 6700, and an FBG extending from the end 6704.

FIG. 67B is cross-sectional view of the pressure sensor housing of FIG.67A, in accordance with this disclosure. In the example shown in FIG.67B, a single diaphragm 6702 can be used, in contrast to a distal discand gasket design, e.g., FIG. 38 at 3804 and 3808. The diaphragm 6702can act as a flexible plate that deflects inwards as the pressure on thesurface increases. The fiber 6706 that includes FBG1 can be held under aslight tension between the bonds 6708 and 6710 similar to previousimplementations. As the pressure increases, the diaphragm 6702 candeflect inwards, thereby releasing some of the tension on the fiber 6706and shifting the wavelength of FBG1 slightly downwards.

The downwards shift in wavelength can be detected by techniquespreviously described and converted to a pressure reading. The thicknessof the diaphragm 6702 can be on the order of several microns to severaltens of microns depending on the material of the diaphragm. Examplediaphragm materials can include a type of glass or polyimide. It can bedesirable for the diaphragm material to behave in the manner of aperfect spring over small deflections. Alternatively, the diaphragm canbehave in a predictable non-linear manner.

One advantage of the diaphragm 6702 is that is shortens the overalllength of the pressure sensor housing and it is also less susceptible tovibrational forces in lateral and longitudinal directions. The disc inthe designs described above can be susceptible to vibration or evengravitational forces as it is a relatively large mass placed in contactwith a gasket with a very small spring constant. This mass can impartunwanted influence on the section of fiber contained within the housing.

For improved performance, the pressure sensor housing 6700 can be stiffto prevent an unwanted bending or other distortions. In some exampleconfiguration, this can mean sizing the inner diameter closely, butwithout interference to the optical fiber 6706. However, thisconfiguration may not be ideal for the diaphragm design as the smallerthe inner diameter, the less deflection is expected for a diaphragm ofgiven material and thickness, which can have a detrimental effect on thedevice sensitivity.

To solve this problem, the pressure sensor housing of FIGS. 67A, 67B caninclude a section, shown at 6712, where the diaphragm 6702 is attachedto the sensor housing 6700 in which the inner diameter is expanded for adistance relatively short compared to the overall length of the housing6700. The shape of the housing 6700 can allow the diaphragm 6702 to havea larger unsupported diameter, which can increase the deflection for agiven applied pressure and thus increase the sensitivity to anacceptable level. The shape of the housing 6712 in FIG. 67B is shown asa tapered flute 6714 but could be other shapes, including, for example,a step to achieve the same desired affect as the deflection of thediaphragm is very small.

One of the advantages achieved by the thinness of the diaphragm 6702presents a challenge with the bonding of the fiber 6706 to the diaphragm6702. In previous designs, e.g., FIG. 38, the bond has been achieved byusing a section of epoxy, shown at 3816. The diaphragm 6702, however,may not present enough length with which to achieve a satisfactory epoxybond. As such, a stopper can be attached to the fiber 6706.

FIG. 67C is cross-sectional view of the pressure sensor housing of FIG.67A, including a fused fiber bond, in accordance with this disclosure.As seen in FIG. 67C, fused fiber bonds 6716, or “stoppers”, can act tostop the fiber 6706 from being pulled through the hole in the diaphragm6706. The stoppers 6716 can be attached to the fiber 6706 in the gapbetween the FBG inside the housing and the FBG outside the housing. Thestoppers can be shaped such that there is only a small area of contactbetween the stopper 6716 and the diaphragm 6702. This is intentional asany significant area of contact can increase the apparent stiffness ofthe diaphragm 6702 and thus reduce the deflection and, by extension, thesensitivity of the pressure sensing function.

Although the shape of the stopper 6716 is depicted as being circular, inother examples, the shape can be a step or taper. There can be a smallamount of sealing material applied between the stopper 6716 and thediaphragm to ensure the interface is airtight. The stopper 6716 can beattached by various methods such as epoxy, glass solder, metal solder orglass fusion.

Epoxy bonds may not be the most suitable technique for ensuring verystable operation of the pressure sensing device. For example, epoxybonds can suffer from mechanical creep, ingress of moisture and othergenerally unstable characteristics. The small nature of the opticalfiber used in the pressure sensing devices of this disclosure meansthere is a very small surface area available on which to realize astable bond. Thus, it can be desirable to use a material or materialsthat are both harder and more stable than epoxy.

One technique to achieve the bond is a glass fusion technique. Insteadof using the same material as is present in the fiber, which can damagethe function of the fiber as it is heated to the temperature necessaryto achieve a glass to glass fusion, a borosilicate glass can be used toattach the stopper. A borosilicate glass has a melt temperaturesignificantly lower than the fused silica glass used in the opticalfiber so it possible to melt and fuse the borosilicate stopper withoutdistorting the optical fiber. A bead or short section of borosilicatecapillary can be threaded over the optical fiber and positioned in thecorrect position. A method of heating can be used that is justsufficient to melt the borosilicate glass without melting the opticalfiber. By controlling the process, the shape of the stopper can becontrolled to leave it more like a flat disc, or by using the naturalsurface tension achieve a more ball like shape. Suitable heating methodscan include, but are not limited to, resistive heating elements, plasmaheating between electrodes, CO2 laser heating, and hot air. It may bedesirable to eliminate all epoxy bonds that are critical to thestability of the device. As such, the borosilicate glass technique canused for the bond 6716 of the optical fiber at the proximal end of thepressure housing as well as the distal bond. As has been mentionedabove, each pressure sensing device may have a unique characteristics.When the device is connected to the pressure system, the parameters thatconstitute the characteristics of the device may need to be transferredto the system so that the correct operation is achieved. Thecharacteristics can also be described as the calibration of the devicerelative to a known reference. The techniques used to transfer thecharacteristics to the pressure sensing system have been described aboveand can include, but are not limited to, manual data entry, RFID chip,barcode scan, disposable chip or read only memory device.

The complete calibration can consist of at least two parts. The firstpart can be a calibration of the lasers within the system or console andthe second part can be the calibration of the disposable device. Thelasers within the system may need to be fully characterized relative toknown standards. These calibrations can include wavelength understandard operating conditions (e.g. fixed temperature and operatingcurrent), and power output, for example.

There can also be a matrix of calibrations that will fully characterizethe lasers so the output conditions are known for any combination ofoperating parameters, e.g., output wavelength and power for a range ofoperating temperatures and operating currents. From this matrix, anyrate of change to output power or wavelength can be determined that willallow calculation of the shift of the laser caused by external stimulus,e.g., change of wavelength relative to operating current when trackingthe optical filter.

The second part of the calibration is the pressure sensing device.During the manufacturing process, the device can be calibrated againstknown standards to determine, amongst other things, the exactwavelength, optical insertion loss and slope of the wavelength responsefor the optical filter. These parameters can be programmed into thecharacteristics for the device so they can be read into any system andthe system can configure itself to work accurately with that device.

It is common when performing medical procedures with this type of deviceto cross calibrate with an external pressure sensor during the initialphase of the procedure. This also serves an important function withverification of procedure efficacy after the procedure is complete asthe reading from the pressure sensing device can be compared to theexternal pressure sensor to make sure the readings are in agreement. Across calibration procedure that includes two main parts, as describedbelow with respect to FIG. 68, can be used for calibration.

FIG. 68 is a flow diagram illustrating an example of a calibrationtechnique, in accordance with this disclosure. First, an initializationoccurs. The initialization can include, for example, applying basicsettings (e.g., factory calibration module), acquiring optical locking,and normalizing/zero settings (block 6800). In addition, theinitialization can include connecting an industry standard referencesensor and obtaining a zero reading on the system/console (block 6802).Next, the pressure sensing device acquires data (block 6804) and theexternal sensor acquires data (block 6806). The initialization uses theparameters of the device characteristics to set the lasers to thecorrect operating conditions and achieve a satisfactory lock on theslope of the optical filter. There may be some small optimization of thelaser operating conditions to ensure best dynamic range.

The first main part (“Calibrate GAIN” in FIG. 68) of the crosscalibration procedure can include matching the difference betweensystolic (maximum) pressure and diastolic (minimum) pressures and thesecond main part (“Apply OFFSET”) can include matching the average ormean pressure. In this example technique, it is assumed that thepressure signal from the external pressure sensor can be compared withthe FFR pressure sensor. The external pressure sensor can be one that iscompliant with the requirements of the published specification ANSI/AAMIBP22:1994/(R) 2011, which relates to a standard bridge type sensor thattypically has a sensitivity of 5 μV/V/mmHg. Depending on theconfiguration of the system there can be a provision for this type ofinput built directly into the FFR console or it will be supplied fromanother piece of equipment.

The first part of the cross calibration can include measuring thedifference between systolic and diastolic pressure over a number ofcycles for the pressure sensing device (block 6810) and the referencesensor (block 6812). Once an accurate number has been established forthe external sensor, this can be used to calibrate the difference forthe FFR sensor. That is, the FFR sensor can be scaled to match theexternal sensor using the systolic/diastolic different (block 6814).This can also be thought of as a gain figure.

The second main part of the cross calibration can include measuring themean of the external sensor over a number of cycles (block 6816),measuring the mean of the FFR pressure sensing device over a number ofcycles (block 6818), and then using this number to set the mean for theFFR pressure sensing device by applying an offset to the pressuresensing device to match the external signal (block 6820). This can bethought of as an offset number. Once these actions have been completed,the FFR sensor is accurately calibrated (block 6822).

There are situations where large changes in the operating conditions ofthe device are possible. These occur mostly when the FFR device is beinginserted into the patient after being calibrated outside the body. Onereason for this is the difference between room temperature (typicallyaround 25° C.) and body temperature (typically around 37° C.). The FBGdevices are sensitive to temperature changes and a change of 12° C. willchange the operating wavelength by approximately 120 pm (10 pm/° C.).This wavelength shift may be too much to correct with a change ofoperating current. The coefficient for the lasers is around 5 pm/mA,which can mean a change of approximately 24 mA, which may not bepossible. One solution is to use the operating temperature of the lasersto account for large changes. A typical laser can have a wavelengthcoefficient of approximately 100 pm/° C. so the operating temperaturecan be adjusted by approximately 1.2° C. to account for the bodytemperature difference and keep the operating current the same.

In one example implementation, the operating current of the laserrequired to keep a lock on the optical filter can be continuallymonitored and then the operating temperature of the laser can bedynamically adjusted to keep the operating current at an optimum value.Another technique that may be advantageous is to have predictivesettings, as shown and described below with respect to FIG. 69.

FIG. 69 is a flow diagram illustrating an example of an offsetprediction technique, in accordance with this disclosure. A crosscalibration to the external sensor at room temperature can be performed(block 6900). If the device is calibrated outside the body (or insidethe body), the system can denote this calibration as a room temperaturecalibration (or body temperature calibration) (block 6902). The systemcan then automatically predict what the appropriate laser parameterswill be once the FFR device is inserted into the body (block 6904) orwhen the FFR device is removed from the body (6906). This can be usefulin achieving rapid locking under certain circumstances. Once the FFRdevice is inserted into the patient the temperature fluctuations aregenerally small, which can coincide with events such as injection ofcontrast agents.

Using the one or more techniques such as disclosed herein, the presentapplicant has described an optical pressure sensing guidewire suitablefor delivery within a body lumen of a patient, e.g., for diagnosticassessment of coronary obstructions. This can advantageously optionallyprovide temperature compensation for sensing pressure within a bodylumen. In addition, the present subject matter can advantageouslymechanically enhance the sensitivity of the fiber to pressure, such aswith an extrinsic arrangement. Further, the present subject matter canutilize Fiber Bragg Gratings in the miniaturized optical fiber therebyresulting in a cost effective and manufacturable design.

This application is related to (1) PCT Application No. PCT/US2013/042769titled, “OPTICAL FIBER PRESSURE SENSOR” to Eberle et al. and filed onMay 24, 2013, and to (2) U.S. patent application Ser. No. 13/902,334titled, “OPTICAL FIBER PRESSURE SENSOR GUIDEWIRE” to Eberle et al. andfiled on May 24, 2013, and to (3) U.S. Provisional Application No.61/791,486 titled, “OPTICAL FIBER PRESSURE SENSOR GUIDEWIRE” to Eberleet al. and filed on Mar. 15, 2013, and to (4) U.S. ProvisionalApplication No. 61/753,221, titled, “OPTICAL FIBER PRESSURE SENSORGUIDEWIRE” to Eberle et al. and filed on Jan. 16, 2013, and to (5) U.S.Provisional Application No. 61/709,781, titled, “OPTICAL FIBER PRESSURESENSOR GUIDEWIRE” to Eberle et al. and filed on Oct. 4, 2012, and to (6)U.S. Provisional Application No. 61/659,596, titled, “OPTICAL FIBERPRESSURE SENSOR GUIDEWIRE” to Eberle et al. and filed on Jun. 14, 2012,and to (7) U.S. Provisional Application No. 61/651,832, titled, “OPTICALFIBER PRESSURE SENSOR GUIDEWIRE” to Eberle et al. and filed on May 25,2012, the entire content of each being incorporated herein by referencein its entirety.

The above detailed description includes references to the accompanyingdrawings, which form a part of the detailed description. The drawingsshow, by way of illustration, specific embodiments in which theinvention can be practiced. These embodiments are also referred toherein as “examples.” Such examples can include elements in addition tothose shown or described. However, the present inventors alsocontemplate examples in which only those elements shown or described areprovided. Moreover, the present inventors also contemplate examplesusing any combination or permutation of those elements shown ordescribed (or one or more aspects thereof), either with respect to aparticular example (or one or more aspects thereof), or with respect toother examples (or one or more aspects thereof) shown or describedherein.

In the event of inconsistent usages between this document and anydocuments so incorporated by reference, the usage in this documentcontrols.

In this document, the terms “a” or “an” are used, as is common in patentdocuments, to include one or more than one, independent of any otherinstances or usages of“at least one” or “one or more.” In this document,the term “or” is used to refer to a nonexclusive or, such that “A or B”includes “A but not B,” “B but not A,” and “A and B,” unless otherwiseindicated. In this document, the terms “including” and “in which” areused as the plain-English equivalents of the respective terms“comprising” and “wherein.” Also, in the following claims, the terms“including” and “comprising” are open-ended, that is, a system, device,article, composition, formulation, or process that includes elements inaddition to those listed after such a term in a claim are still deemedto fall within the scope of that claim. Moreover, in the followingclaims, the terms “first,” “second,” and “third,” etc. are used merelyas labels, and are not intended to impose numerical requirements ontheir objects.

In an example, the circuits described herein, including its variouselements discussed in this document, can include a combination ofhardware and software. For example, one or more portions, elements, orcircuits included can be implemented, such as using anapplication-specific circuit constructed to perform one or moreparticular functions or a general-purpose circuit programmed to performsuch function(s). Such a general-purpose circuit (e.g., a processorcircuit) can include, but is not limited to, a microprocessor or aportion thereof, a microcontroller or portions thereof, and aprogrammable logic circuit or a portion thereof, such as configured toexecute or otherwise perform instructions stored within or on a mediumreadable by a machine or device, such as a memory circuit.

Method examples described herein can be machine or computer-implementedat least in part. Some examples can include a computer-readable mediumor machine-readable medium encoded with instructions operable toconfigure an electronic device to perform methods as described in theabove examples. An implementation of such methods can include code, suchas microcode, assembly language code, a higher-level language code, orthe like. Such code can include computer readable instructions forperforming various methods. The code may form portions of computerprogram products. Further, in an example, the code can be tangiblystored on one or more volatile, non-transitory, or non-volatile tangiblecomputer-readable media, such as during execution or at other times.Examples of these tangible computer-readable media can include, but arenot limited to, hard disks, removable magnetic disks, removable opticaldisks (e.g., compact disks and digital video disks), magnetic cassettes,memory cards or sticks, random access memories (RAMs), read onlymemories (ROMs), and the like.

The above description is intended to be illustrative, and notrestrictive. For example, the above-described examples (or one or moreaspects thereof) may be used in combination with each other. Otherembodiments can be used, such as by one of ordinary skill in the artupon reviewing the above description. The Abstract is provided to complywith 37 C.F.R. § 1.72(b), to allow the reader to quickly ascertain thenature of the technical disclosure. It is submitted with theunderstanding that it will not be used to interpret or limit the scopeor meaning of the claims. Also, in the above Detailed Description,various features may be grouped together to streamline the disclosure.This should not be interpreted as intending that an unclaimed disclosedfeature is essential to any claim. Rather, inventive subject matter maylie in less than all features of a particular disclosed embodiment.Thus, the following claims are hereby incorporated into the DetailedDescription as examples or embodiments, with each claim standing on itsown as a separate embodiment, and it is contemplated that suchembodiments can be combined with each other in various combinations orpermutations. The scope of the invention should be determined withreference to the appended claims, along with the full scope ofequivalents to which such claims are entitled.

1-3. (canceled)
 4. An optical fiber connector assembly configured tocouple a proximal end of a guidewire assembly having a first opticalfiber to a second optical fiber, the connector assembly comprising: aconnector housing having a proximal end, a distal end, a bore extendingtherethrough; a distal ferrule defining a distal ferrule lumenconfigured to receive the first optical fiber, the distal ferrulepositioned within the bore and configured to couple to a tube, the tubecoupled to the proximal end of the guidewire ferrule; a proximal ferrulepositioned within the bore and abutted against the distal ferrule,wherein the proximal ferrule includes a proximal ferrule lumenconfigured to receive the second optical fiber, wherein an end of thesecond optical fiber is configured to align with and butt against an endof the first optical fiber; and a split sleeve disposed about at least aportion of the distal ferrule and at least a portion of the proximalferrule.
 5. The optical fiber connector assembly of claim 4, wherein thedistal end includes a tapered portion to receive the guidewire.
 6. Theoptical fiber connector assembly of claim 4, wherein the first opticalfiber has a diameter of between about 20 micrometers and about 80micrometers.
 7. The optical fiber connector assembly of claim 4, whereinthe second optical fiber has a diameter of about 125 micrometers.
 8. Theoptical fiber connector assembly of claim 4, wherein the distal ferrulehas a first portion having a first diameter and a second portion havinga second diameter smaller than the first diameter, wherein the tube isconfigured to receive the second portion of the distal ferrule.
 9. Theoptical fiber connector assembly of claim 4, wherein the first opticalfiber extends from a periphery of the guidewire to and through a centeraxis lumen of the distal ferrule.
 10. The optical fiber connectorassembly of claim 4, wherein the tube is metal.
 11. The optical fiberconnector assembly of claim 4, further comprising: a capillary tubehaving a capillary lumen, the capillary tube configured to be positionedwithin the distal ferrule lumen, wherein the capillary lumen isconfigured to receive the first optical fiber.
 12. The optical fiberconnector assembly of claim 11, wherein the capillary tube is bonded tothe distal ferrule.
 13. The optical fiber connector assembly of claim 11wherein the first optical fiber is bonded to the capillary tube.
 14. Theoptical fiber connector assembly of claim 4, in combination with theguidewire assembly.
 15. The optical fiber connector assembly of claim14, wherein the guidewire assembly includes an optical fiber pressuresensor coupled to the first optical fiber.
 16. The optical fiberconnector assembly of claim 4, further comprising: an optical fiber stubhaving a first end and a second end, wherein the end of the secondoptical fiber configured to align with and butt against the end of thefirst optical fiber is fusion spliced to the first end of the opticalfiber stub and the second end of the optical fiber stub is configured toalign with and butt against the end of the first optical fiber.